Eco-efficiency for the
Dairy Processing Industry
Prepared by: The UNEP Working Group for Cleaner Production in the Food Industry Environmental Management Centre, The University of Queensland, St Lucia Penny Prasad, Robert Pagan, Michael Kauter and Nicole Price Telephone: + 61 7 3365 1432 E-mail:
[email protected] Sustainable Business Level 9, 121 Walker Street, North Sydney Patrick Crittenden Telephone: + 61 2 4268 0839 E-mail:
[email protected] This manual was produced as part of the Dairy Processing Eco-efficiency Project (DAV447) and was funded by Dairy Australia. DAIRY AUSTRALIA Level 5, IBM Tower 60 City Road Southbank Victoria 3006 Australia Telephone: + 61 3 9694 3777 Fax: + 61 3 9694 3733 www.dairyaustralia.com.au AUGUST 2004
Acknowledgements Dairy Australia and the UNEP Working Group for Cleaner Production are grateful to the following individuals for their participation in this project and the development of the manual.
Steering Committee Ross Nicol
Dairy Australia
Susan Blacklow
National Foods Limited
Janis Cecins
Dairy Farmers
Patrick Crittendon
Sustainable Business
Richard Tomsett
Bonlac Foods Limited
Neil Van Buuren
Murray Goulburn Co-operative Company Limited
Mike Weeks
Dairy Processing Engineering Centre
Karin Harding
Tatura Milk Industries Limited
Peter Gross
Bonlac Foods Limited
Adrian Poon
Bonlac Foods Limited
Anthony Best
Warrnambool Cheese and Butter Factory Company Limited
Margaret Berbers
Parmalat Australia Limited (On behalf of Justine Young)
Mike Jones
Queensland Department of Primary Industries and Fisheries
Bob Pagan
UNEP Working Group for Cleaner Production in the Food Industry
Penny Prasad
UNEP Working Group for Cleaner Production in the Food Industry
Disclaimer: While every attempt has been made to ensure that the information in this publication is correct at the time of printing, errors can occur. The information is provided as general information only. Specific issues relevant to your workplace should be considered in light of this and on an individual basis. The information provided in this publication should not be construed as legal advice. You should consult with professional advisers familiar with your particular factual situation for advice concerning specific environmental requirements.
Cover images: Dairy Australia, Dairy Processing Engineering Centre and UNEP Working Group for Cleaner Production.
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ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
Contents 1
Introduction 1.1
Profile of the Australian dairy processing industry
1
1.2
Environmental challenges
3
1.2.1
Compliance and legislation
3
1.2.2
Water supply and pricing
3
1.2.3
Wastewater discharge costs
3
1.2.4
Energy and energy supply costs
4
1.2.5
Solid waste management
5
1.2.6
Packaging
6
1.3
1.3.1
Reasons for adopting eco-efficiency
7
1.3.2
How to carry out an eco-efficiency assessment
7
Eco-efficiency and environmental management
8
1.5
Food safety and HACCP
9
1.6
Key performance indicators
9
1.7
Achieving best practice in dairy processing
10
1.7.1
10
Characteristics of a company that is aiming for best practice
Summary
12
Making eco-efficiency happen in your organisation 2.1
Barriers to eco-efficiency
13
2.2
Avenues for supporting the implementation of eco-efficiency
14
2.3
The Murray Goulburn experience
15
2.3.1
Building skills, knowledge and support through site-based teams
15
2.3.2
Raising management awareness of the benefits of eco-efficiency
17
2.4
3
6
1.4
1.8
2
What is eco-efficiency?
Summary
18
Water 3.1
3.2
CONTENTS
Overview of water use
19
3.1.1
Water use in dairy factories
19
3.1.2
The true cost of water
20
3.1.3
Measuring water consumption
22
3.1.4
Increasing staff awareness and involvement
23
Reducing demand for water: processing
24
3.2.1
24
Optimising rate of water flow
iii
3.3
3.4
24
3.2.3
Leaks
25
Reducing demand for water: cleaning
26
3.3.1
Design and selection of processing equipment and process layout
26
3.3.2
Dry cleaning
26
3.3.3
Trigger-operated controls for hoses
26
3.3.4
High-pressure cleaning systems
27
3.3.5
Clean-in-place systems
27
3.3.6
Scheduling or modifying product changeovers
30
3.3.7
Crate washers
30
Reducing demand for water: utilities
31
3.4.1
Blowdown in cooling towers and boilers
31
3.4.2
Cooling tower operation
31
3.4.3
Equipment sealing water
32
Ancillary water use
32
3.6
Stormwater
33
3.7
Water recycling and reuse
34
3.7.1
Condensate recovery
34
3.7.2
Use of membranes for water recovery
38
Wastewater
39
3.8.1
Treatment of wastewater
39
3.8.2
Selection of a wastewater treatment system
40
3.8.3
Reuse of treated wastewater for irrigation
41
Energy 4.1
Overview of energy use
43
4.1.1
45
The cost of energy
4.2
Energy management
46
4.3
Reducing the demand for steam and hot water
47
4.3.1
Evaporation
47
4.3.2
Membrane concentration
49
4.3.3
Spray drying
49
4.3.4
Boiler operation
51
4.3.5
Steam delivery
54
4.3.6
High-efficiency boilers
56
Reducing the demand for electricity
57
4.4.1
Refrigeration systems
57
4.4.2
Compressed air systems
61
4.4.3
Homogenisers
64
4.4
iv
Efficient process control
3.5
3.8
4
3.2.2
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
4.5
4.6
4.7
5
4.4.4
Motors
65
4.4.5
Lighting
67
4.4.6
Air-conditioning and air-handling systems
69
Heat recovery
71
4.5.1
Pinch technology
71
4.5.2
Stratified storage tanks
71
4.5.3
Improving the efficiency of pasteurisers and sterilisers
71
Alternative sources of energy
73
4.6.1
Biofuels
73
4.6.2
Solar energy
75
4.6.3
Wind energy
75
Cogeneration
76
4.7.1
Types of cogeneration
76
4.7.2
Applicability of cogeneration to the dairy processing industry
77
Yield optimisation and product recovery 5.1
Overview
78
5.1.1
Sources of product loss
78
5.1.2
The cost of lost product
79
5.1.3
Further reading
83
5.2
Waste minimisation
83
5.3
Improving plant layout and design
84
5.4
Efficient processing and process control
85
5.5
Milk receival, initial processing and storage
86
5.6
Minimising product waste during processing
87
5.6.1
Optimising start-up and shutdown procedures and changeovers
87
5.6.2
Optimising product formulation
87
5.6.3
Production scheduling
88
5.6.4
Separator de-sludge optimisation
88
5.6.5
Minimising loss of cheese fines
89
5.6.6
Spray dryers and evaporation
90
5.6.7
Product recovery during filling
92
5.7
5.8
CONTENTS
Maximising product recovery during cleaning
92
5.7.1
Clean-in-place (CIP) systems
92
5.7.2
Pigging
93
Use of membranes for recovery of resources
94
v
6
Solid waste reduction and value adding 6.1
7
96
6.1.1
Sources of solid waste
96
6.1.2
The true cost of solid waste
97
6.1.3
Solid waste management
98
6.1.4
Supply chain management
99
6.2
Value adding
100
6.3
Recycling and reuse
102
6.3.1
Onsite reuse of solid waste
102
6.3.2
Establishing a solid waste recycling system
102
6.4
Reducing the impacts of packaging
105
6.5
Disposal of solid organic waste
107
6.5.1
Animal feed
107
6.5.2
Composting
108
6.5.3
Soil injection and direct landspreading
109
Chemical use 7.1
7.2
7.3
7.4
vi
Overview
Overview of chemical use
110
7.1.1
Cleaning
110
7.1.2
Detergents, acids and sanitisers
112
7.1.3
Water quality
114
7.1.4
True cost of chemicals
114
7.1.5
Environmental impacts of chemicals
115
Optimising chemical use
115
7.2.1
Chemical types and blends
116
7.2.2
Chemical concentrations
117
7.2.3
Cleaning cycle times
118
7.2.4
Control instrumentation
118
7.2.5
Effect of temperature
118
7.2.6
Chemical recovery
119
7.2.7
Operator competency and safety
120
7.2.8
Equipment operation and maintenance
120
Chemical alternatives
121
7.3.1
Biodegradable chemicals
121
7.3.2
Enzyme-based detergents
122
7.3.3
Reduced phosphate, nitric and sodium blends
123
Chemical treatment of boilers, cooling water and condensate water
124
7.4.1
124
Boiler water treatment
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
7.5
7.6
7.7
CONTENTS
7.4.2
Cooling water treatment
124
7.4.3
Condensate water treatment
124
Alternatives to chemical use
125
7.5.1
Ozone
125
7.5.2
Ultraviolet light
125
Supply and handling of chemicals
126
7.6.1
Supply agreements and performance-based contracts
126
7.6.2
Bulk supply of chemicals
126
Further reading
127
vii
Tables 1
3
4
Introduction Table 1.1
Major Australian dairy manufacturing sites
2
Table 1.2
Typical key performance indicators for a dairy processor
9
Water and wastewater Table 3.1
Water to milk intake ratios (L/L)
20
Table 3.2
Water supply costs in dairy processing regions
21
Table 3.3
Example of the true cost of ambient and hot water ($/kL)
22
Table 3.4
Cost of water loss from leaking equipment
25
Table 3.5
Water appliance ratings
33
Table 3.6
Comparison of water efficient products with non-rated products
33
Table 3.7
Suitability of saline wastewater for irrigation
42
Table 4.1
Proportions of electricity and thermal energy use
43
Table 4.2
Total energy use — electrical and thermal
44
Table 4.3
Typical costs for primary energy sources
45
Table 4.4
Typical fuel costs for steam production
45
Table 4.5
Typical fuel costs for direct heating of water with electricity or gas from 20°C
Energy
to 84°C
46
Table 4.6
Energy consumption of multi-effect evaporators and vapour recompression
48
Table 4.7
Optimum flue gas composition
51
Table 4.8
Fuel savings from installing online oxygen trim control
52
Table 4.9
Heat loss from steam lines
56
Table 4.10
Cost of compressed-air leaks
62
Table 4.11
Cost and energy savings that can be made by reducing air pressure
63
Table 4.12
Energy and costs savings from reducing the temperature of compressor inlet air
64
Table 4.13
Payback periods for purchasing high-efficiency motors
65
Table 4.14
Cost comparisons for oversized motors
65
Table 4.15
Savings due to installation of variable speed drives
66
Table 4.16
Comparison of different types of lighting
68
Table 4.17
Sample methane and energy yields from biogas digestion for an ice-cream factory in New South Wales
viii
73
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
5
6
Yield optimisation and product recovery Table 5.1
Sources of product loss in dairy processing plants
79
Table 5.2
Indicative wastewater characteristics from dairy processing plants
80
Table 5.3
Effluent to milk ratio (L/L)
81
Table 5.4
Trade waste charges in various regions
82
Table 5.5
Comparison of trade waste charges for Plant A
82
Table 5.6
Membranes used in the dairy industry
94
Solid waste reduction and value adding Table 6.1
7
TABLES
Sources of solid waste in dairy processing plants
97
Chemical use Table 7.1
Characteristics of typical soiling found in the dairy industry
111
Table 7.2
Types of chemicals used in the dairy industry
113
Table 7.3
Comparison of inorganic and organic acids
122
ix
Figures
x
Figure 1.1
Milk production by state 2002–03
2
Figure 1.2
Utilisation of manufacturing milk 2002–03
2
Figure 1.3
Waste minimisation hierarchy
5
Figure 1.4
Method of undertaking an eco-efficiency assessment
8
Figure 3.1
Breakdown of water use of a market milk processor
20
Figure 4.1
Energy cost breakdown by area — milk plant
44
Figure 4.2
Energy cost breakdown by area — powder, cheese and whey plant
44
Figure 4.3
Single effect falling film evaporator schematic
48
Figure 6.1
Waste minimisation hierarchy
99
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
1
Introduction This manual has been developed to help the Australian dairy processing industry increase its competitiveness through increased awareness and uptake of eco-efficiency. The manual seeks to consolidate and build on existing knowledge, accumulated through projects and initiatives that the industry has previously undertaken to improve its use of raw materials and resources and reduce the generation of wastes. Where there is an existing comprehensive report or publication, the manual refers to this for further information. Eco-efficiency is about improving environmental performance to become more efficient and profitable. It is about producing more with less. It involves applying strategies that will not only ensure efficient use of resources and reduction in waste, but will also reduce costs. This chapter outlines the environmental challenges faced by Australian dairy processors. The manual explores opportunities for reducing environmental impacts in relation to water, energy, product yield, solid and liquid waste reduction and chemical use.
1.1
Profile of the Australian dairy processing industry The Australian dairy processing industry makes a significant contribution to the national economy. In terms of value, processed dairy products are the third-largest exported good in Australia after grains and meat, contributing 12% or $3.27 billion to Australia’s exports (DAFF 2003). In 2002–03 the industry had a farmgate value of $2.8 billion with an ex-factory turnover estimated at more than $8.5 billion and a value-added component of $1.6 billion. The entire dairy industry employs almost 200 000 people with 19 000 of these employed in dairy manufacturing (DAFF 2003 and Dairy Australia 2003). Milk production is concentrated in the south-east corner of Australia, with Victoria, Tasmania and South Australia accounting for 77% of total output, producing approximately 10 300 million litres in 2002–03. The dairy industry can be divided into two distinct sectors: the market milk sector, producing milk for drinking and products with a short shelf-life; and the manufacturing sector, yielding products with a long shelf-life suitable for export. The volume of drinking milk produced has remained relatively static over recent years, accounting for nearly 19% of total milk production. The proportion of market milk to manufacturing milk in the total product mix differs significantly between states, as shown in Figure 1.1.
INTRODUCTION
1
Figure 1.1
Milk production by state 2002–03 100% 80% 60% 40% 20% 0% NSW
Vic
Qld
Market milk
SA
WA
Tas
Aust
Manufacturing milk
Source: Dairy Australia 2003
In Australia milk is processed by farmer-owned cooperatives and by public and private companies. The largest cooperatives — Murray Goulburn Co-operative Ltd, Bonlac Supply Company and the Dairy Farmers Group — account for more than 60% of all milk production and more than 70% of all milk used for manufacturing. Multinational dairy companies operating in Australia include Fonterra, Parmalat, Nestlé, Kraft and Snow Brand. In addition there are public companies such as National Foods Ltd and private companies such as Warnambool Cheese and Butter, and Tatura Milk Industries. As Table 1.1 shows, there are 70 major dairy manufacturing sites across Australia, 51 of which are in rural areas. The largest cooperative accounts for 30% of Australia’s milk production, while there are smaller cooperatives that produce volumes between 100 and 600 million litres (Dairy Australia 2003). Figure 1.2 shows the utilisation of manufacturing milk by major process lines. Table 1.1
Major Australian dairy manufacturing sites
Figure 1.2
Utilisation of manufacturing milk 2002–03
State
No. of sites Capital city
Rural region
NSW
3
9
Vic.
7
24
Qld
3
6
SA
2
4
WA
2
3
Tas.
1
5
NT
1
–
19
51
Australia
Other 15%
Cheese 42% Butter/skim milk powder 23%
Casein/butter 5%
Whole milk powder 15%
Source: Dairy Australia 2003
2
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
1.2
Environmental challenges
1.2.1
Compliance and legislation Environmental legislation that regulates Australian dairy processing plants is implemented by authorities such as state environmental protection agencies (EPAs) and local councils. Dairy processors are generally required to have licences for emissions to air and surface waters and the disposal to land of some solid and liquid wastes such as sludge and treated wastewater. Disposal of wastewater to the sewerage system is regulated by local councils or local water authorities.
1.2.2
Water supply and pricing Over the entire life cycle of dairy manufacture, including milk production on farm, transportation and dairy processing, 99% of the total water consumption can be attributed to the farm (Lunde et al. 2003). For the industry as a whole, therefore, efforts to make major gains in reducing the environmental impacts of water consumption should be focused on the farm. Nevertheless, there are gains to be made by dairy processors in minimising water consumption within factories. Depending on the product mix, dairy processing plants can use substantial volumes of water for equipment cleaning, cooling towers, boilers and other processes. Water supply to dairy processing plants varies according to location, but may be from town water, bores, rivers, dams or irrigation channels. Some factories are required to install large storage reserves to cater for periods of non-supply; for example Bonlac’s Stanhope factory must store its entire winter supply to allow maintenance of water channels by the local water board. As increasing pressure is placed on limited water reserves, government bodies and water authorities are actively seeking to promote greater water efficiency and are encouraging water conservation strategies and incentives. For example, Brisbane Water recently introduced a scheme for providing water rebates to large users of water that have developed and implemented water management plans (Cameron Jackson 2004, pers. comm.) and Sydney Water is encouraging large users of water to reduce water consumption through involvement in the ‘Every Drop Counts’ business partnership program (Sydney Water 2004). Water supply costs for Australian processors are vary according to the region, ranging between 20c/kL for a North Queensland processor and $1.28/kL for a processor in South-East Queensland. Water supply costs are discussed further in Chapter 3. Many water authorities are now progressively introducing a user-pays charging system to recover the full cost of supplying water to the consumer, in order to encourage water conservation and to cut costs.
1.2.3
Wastewater discharge costs Wastewater discharge costs vary according to the region, and according to whether the waste is being discharged to land, surface waters or the sewerage system. Plants discharging treated wastewater to municipal sewerage systems face the highest costs. Most water authorities charge on the basis of the organic loads (BOD/COD) and include a separate volumetric charge. However, there are exceptions to this, such as plants
INTRODUCTION
3
discharging to Sydney Water’s direct ocean outfalls, where the charging structure is based only on the mass load (in kg) of waste components. Some utility operators have introduced additional charges for nitrogen, phosphorus and sodium loads and these charges are increasing. For example, Ipswich Water in Queensland currently charges 80c/kg for nitrogen and $3/kg for phosphorus. These charges are expected to increase to more than $2/kg and $9/kg over the next few years (Mark Sherson 2004, pers. comm.). Many utility operators also charge for oil and grease content and suspended solids. The charge structure is affected by the processes used by the treatment plants, and by the costs incurred in handling different components of the wastewater. Charging structures can also be used to ‘send a message’ to customers and encourage measures such as waste minimisation to reduce loads. Factories that dispose of effluent directly to land generally do not pay disposal charges, but must meet licence conditions for the quality of effluent with respect to components such as mineral content, salt level, BOD or COD, phosphorus, nitrogen, and oil and grease. Full cost recovery charging has not so far been applied to sewer discharges, but this situation is changing. Many local authorities and water boards, especially those in metropolitan areas, are in the process of formulating charging systems that will progressively increase wastewater discharge fees on a user-pays basis until something approaching full cost recovery is achieved.
1.2.4
Energy and energy supply costs As with most Australian industries, dairy companies rely on fossil fuels — particularly coal-generated electricity, coal and natural gas — for their energy supply. National greenhouse abatement initiatives such as the Greenhouse Challenge and the Australian Renewable Energy Certificate scheme have been launched in recent years to increase awareness of environmental issues and encourage the more efficient and sustainable use of energy. As yet, only a small number of dairy companies have joined these schemes. Nevertheless, Australian dairy processors appear to be relatively energyefficient compared with dairy processing companies internationally. A recent survey of Australian dairy processors has shown that energy consumption per unit of production is comparable to, if not better than, energy consumption in European dairies (see Chapter 4, ‘Energy’). The dairy manufacturing industry has radically improved its energy efficiency over the last 20 years (in some cases by as much as 50%) through industry-wide upgrading of equipment and the closing of smaller, less efficient factories (Lunde et al. 2003). The industry could further explore the use of renewable energy, and an obvious means is through the use of biogas (from anaerobic digesters) to supplement energy supplies. Cogeneration systems have been investigated but to date have been found not to be financially viable. The national energy supply market (electricity and gas) has been progressively deregulated over the last decade. Deregulation in the electricity industry began in Victoria in 1994 and has spread to most states, giving dairy companies a choice of retail companies for their supply of electricity. The low cost of energy and the lack of mechanisms to control demand in Australia are seen as among the main factors
4
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
inhibiting the adoption of more energy-efficiency practices (UNEP 2002). Energy is typically the greatest of all utility costs, despite the low unit cost, so significant savings are possible; it therefore makes economic sense for dairy processors to minimise energy consumption. A medium to large dairy processing site could typically spend $2–3 million on energy costs per year, so a possible 10% reduction in energy costs can be a significant incentive to reduce energy use.
1.2.5
Solid waste management Solid wastes generated by dairy processors include: • packaging waste such as cardboard, cartons, paper and plastic • organic waste such as sludge and reject product • building and maintenance wastes • office waste. Dairy processing plants in city areas are generally well serviced by waste disposal and recycling companies, so it is usually more profitable for a company to segregate and recycle wastes than to dispose of waste to landfill. Processing plants in regional areas may experience some difficulties until waste services are developed and expanded. Organic waste is generally disposed of as animal feed, applied to farm land as fertiliser, composted, or digested to produce biogas. For dairy processors, solid waste disposal costs can be a relatively minor component of total operating costs. It is, however, an area where employees at all levels can contribute and immediately see results, and this can be a good start in encouraging employees to be more environmentally aware and participate in company-wide initiatives. The waste minimisation hierarchy shown below in Figure 1.3 represents a sequential approach to reducing solid waste — with steps to avoid, reduce, reuse, recycle and lastly treat and dispose waste. This is discussed further in Chapter 6, ‘Solid waste reduction and value adding’.
Figure 1.3
The waste minimisation hierarchy
Avoid
Reduce
Reuse
Recycle
Treat and dispose
INTRODUCTION
5
1.2.6
Packaging Dairy processors face increasing pressure to develop and use packaging that reduces the consumption of resources, enables reuse or recycling, and minimises landfill disposal. The importance placed on packaging may reflect the strong increase in awareness resulting from the National Packaging Covenant (NPC), launched in 1999. The NPC encourages voluntary actions by signatory companies to reduce packaging waste, and is underpinned by regulation in all states to include non-signatories. In some cases packaging initiatives are driven by the requirements of export customers. Most dairy processing companies are signatories to the NPC. Eco-efficiency opportunities for reducing packaging waste are included in Chapter 6.
1.3
What is eco-efficiency? Eco-efficiency is a ‘win–win’ business strategy that helps companies save money and reduce their environmental impact. Eco-efficiency means increasing process efficiencies and reducing environmental impact, for example by reducing the use of goods and services, enhancing recyclability, and maximising the use of renewable resources. The World Business Council for Sustainable Development has identified a range of ways companies can improve their eco-efficiency (WBCSD 2000). Companies can: • reduce material intensity of goods and services • reduce energy intensity of goods and services • reduce toxic emissions • enhance material recyclability • maximise use of renewable resources • extend product durability • increase efficiency in the use of goods and services. Eco-efficiency is often pursued through approaches and ‘tools’ such as cleaner production, environmental management systems, life-cycle assessment and design for the environment. These tools help companies identify opportunities to improve resource efficiency and reduce environmental impacts. Eco-efficiency involves systematically evaluating existing practices to identify opportunities for improvement. The ultimate goal is to avoid the use of a resource or eliminate the production of a waste altogether. Failing this, smarter solutions to existing practices are investigated, which aim to reduce, reuse, recover or recycle
6
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
resources and waste. Eco-efficiency opportunities can usually be categorised into five main groups: housekeeping improvements, product modification, input substitution, process improvements, and onsite recycling.
1.3.1
Reasons for adopting eco-efficiency There are many reasons for dairy processors to adopt eco-efficiency, including: • to reduce operating costs and improve profitability • to reduce energy, water supply and solid waste costs • to overcome water allocation restrictions • to reduce wastewater treatment and/or disposal costs • to reduce the effect of rising wastewater discharge fees in the future • to comply with tightening air emission standards • to help in developing waste minimisation plans (e.g. water and waste management plans, National Packaging Covenant or Greenhouse Challenge plans) • to create an ‘environmentally friendly’ image and gain competitive edge • to improve relations with environmental regulators and ensure compliance with regulations • to add value in the adoption of an environmental management system. The best starting point for any company that wants to improve its eco-efficiency is to conduct an eco-efficiency assessment. This process is described in the next section.
1.3.2
How to carry out an eco-efficiency assessment A method for carrying out an eco-efficiency assessment is shown schematically in Figure 1.4. This method has been adapted from the UNEP Environmental management tools — cleaner production (UNEPTIE 2003) and outlines six main steps: planning and organisation, pre-assessment, assessment, evaluation and feasibilty, implementation and continuous improvement. An eco-efficiency self-assessment guide can be found as part of the Eco-efficiency toolkit for the Queensland food processing industry (UNEP 2004). There are also dairy-specific publications that describe waste minimisation programs — in particular, Environmental management tools for the dairy processing industry, Parts 1 and 2 (Jones et al, 2002).
INTRODUCTION
7
Figure 1.4
Method of undertaking an eco-efficiency assessment
Step A Planning and organisation
Step B Pre-assessment
a. Gain management commitment b. Form a project team c. Plan the assessment
a. Develop process flow chart & identify inputs and outputs b. Carry out ‘walk through’ inspection
a. Quantify inputs and outputs Step C Assessment
Step D Evaluation and feasibility
Step E Implementation
Step F Continuous improvement
b. Establish perfomance indicators an set targets for improvement c. Conduct water, energy and waste audits d. Identify eco-efficiency opportunities
a. Preliminary evaluation b. Economic and technical evaluation
a. Prepare an action plan b. Implement eco-efficiency options
a. Monitor and review performance
Source: Adapted from UNEP, Environmental Management Tools — Cleaner Production Assessment, 2003
1.4
Eco-efficiency and environmental management An environmental management system (EMS) is a documented set of procedures that identifies the impacts of a company on the environment and defines how they are managed on a daily basis. It is an ongoing process that demonstrates the company’s commitment to ensuring a good standard of environmental management. A company may choose to obtain third-party certification of its EMS to the ISO14001 standard. To date, few Australian dairy processors have an ISO14001-certified EMS; but there are some larger processors, particularly those that compete with export markets, that have gained certification. Some processors have an effective corporate EMS that is not certified.
8
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
Like eco-efficiency, environmental management is a process of continual improvement with documented management and action plans. An eco-efficiency assessment identifies those areas of greatest impact and seeks to suggest financially attractive options to control or reduce these impacts. An eco-efficiency assessment should not be undertaken separately from an EMS; instead it should complement it, with the outcomes of the assessment being incorporated into EMS action or audit plans.
1.5
Food safety and HACCP ‘Hazard analysis critical control point’ (HACCP) is commonly used throughout the dairy processing industry to identify and manage those steps in a processing operation that may pose a risk to food safety and quality. Proactive preventive procedures and controls are established to prevent or manage these risks. It is essential that any eco-efficiency opportunities that are identified for a dairy company do not adversely affect food safety and quality. Water recycling is an example of an eco-efficiency opportunity where increased risk (or perceived risk) can be a barrier to its adoption. New procedures set in place as a result of an eco-efficiency assessment may need to be included and managed by the HACCP system. Conversely, a HACCP program may identify issues and link in with an eco-efficiency assessment.
1.6
Key performance indicators Typical eco-efficiency key performance indicators (KPIs) for dairy processors are shown in Table 1.2. The development of benchmarks is an effective way to encourage continuous improvement within or between companies. By comparing one plant’s KPIs with those of similar processing plants, it will be possible to identify areas where there is scope for improvement. KPIs for water and energy consumption are outlined in later chapters. KPIs can be linked to staff incentive schemes and to other management programs. They are a useful, easily understood, spin-off from an eco-efficiency program and can help in prioritising overall efficiency.
Table 1.2
Typical key performance indicators for a dairy processor
INTRODUCTION
Component
KPI
Product yield
kL or tonnes product per kL raw material consumed
Water
kL consumed per kL or tonne product
Water-to-milk ratio
kL water per kL raw milk processed
Water reuse %
kL water reused per kL total water used
Energy
MJ consumed per kL or tonne product
Energy-to-milk ratio
MJ energy per kL raw milk processed
Wastewater
kL generated per kL or tonne product
Solid waste
kg generated per kL or tonne product
9
1.7
Achieving best practice in dairy processing Subsequent chapters describe numerous eco-efficiency opportunities that are available to the dairy processing industry. Many of the opportunities described are not new, and could be considered as good operating or engineering practice; and they have been undertaken to some degree by most leading dairy processing companies. Where possible, benchmark figures have been provided for aspects such as water and energy consumption and wastewater volumes and quality. While the question of ‘best practice in dairy processing’ cannot be directly quantified within the scope of this document, the following points attempt to describe the characteristics of a dairy processing company and operation that is headed towards best practice. Ideally, the adoption of best-practice technologies, procedures and initiatives should be considered during the design and planning stages of a plant. A holistic approach should also be taken in deciding what is the most appropriate technology or plant design. For example, if a factory in a regional area has the option to irrigate, it may not be sensible for it to treat wastewater to potable water standards.
1.7.1
Characteristics of a company that is aiming for best practice General: • a multi-use clean-in-place (CIP) system with the use of membranes to recover product, chemicals and water • integrated process control software that enables trending of key variables and generates customised reports for different purposes; able to be accessed by management from office workstations; and uses programs that interface with accounting, inventory, maintenance and quality systems • membrane plants for the recovery of condensate, cleaning chemicals and, in some circumstances, whey proteins.
Product yield: • inline monitoring of key contaminant levels — COD, EC, pH, turbidity, protein, fat • effectively designed pigging systems for key product lines • CIP-able bag houses for spray dryers.
Water usage: • a detailed water balance or model that identifies the volume of water used in each area • water meters installed at strategic locations through the plant, and a system for regularly monitoring and reporting water consumption • inline probes to detect product–water interfaces
10
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
• segregation of wastewater streams, with appropriate-quality streams reused rather than all streams being sent to the waste treatment process or to effluent; diversion of wastewater streams to different stages of the treatment process as required, using online monitoring of chemical oxygen demand (COD) or other parameter • in powder plants, a condensate recovery system for ‘cow water’ that reuses 90–100% of available condensate • a knowledge of the typical quantity and quality of wastewater streams at all times during processing using online and traditional monitoring techniques • recirculation or reuse of pump sealing water • zero discharge of wastewater to sewer for dairy processors in regional areas that have the opportunity to use water for irrigation.
Energy usage: • a detailed energy balance or model that identifies what quantity of energy is used in each area • a system for the regular monitoring and reporting of energy consumption • in powder plants, mechanical vapour recompression evaporators and multi-stage dryers • high-efficiency boilers with recuperators and economisers for recovery of heat to pre-heat flue gas and boiler feed water • biogas recovery, with biogas used to supplement energy consumption • cogeneration plants that export excess electricity to the grid • efficient demand-management systems, including load shedding, to reduce peak demand • efficient refrigeration systems that utilise state-of-the-art control systems, variable speed drive (VSD) compressors, heat recovery and ice bank storage where applicable • high-efficiency motors of at least 90% efficiency • efficient lighting systems that take advantage of natural light and automatically switch off or dim according to lighting needs • pinch analysis of dairy factories to identify possible areas for improvement in heating and cooling duties.
Chemicals: • the use of enzyme-based and chemicals with reduced rates of phosphate and nitrogen • the holistic use of chemicals with consideration of the impact of wastewater disposal, particularly in regard to irrigation and salinity issues • clean-in-place systems incorporating chemical recovery.
INTRODUCTION
11
Future technologies: • the use of alternative renewable fuels such as solar and wind energy • the possible use of ozone for the treatment of wastewater streams • active noise control of spray dryers to control noise pollution.
1.8
Summary In past years, the dairy processing industry has undertaken various resource management and waste minimisation programs to increase operating efficiencies. These programs have been undertaken on a corporate basis or for individual sites driven by a few motivated managers. Many of the 70 dairy processing plants across Australia are well over 50 years old, with processing operations that have grown in size, with a combination of old and new equipment and technologies, and with workforces of various levels of experience. For these plants, there are numerous eco-efficiency opportunities that can be taken up. These range from simply improving housekeeping through to investing capital to upgrade or replace existing equipment. The chapters that follow describe some of the challenges and opportunities that are available to the industry.
12
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
2
Making eco-efficiency happen in your organisation ‘Doing more with less’ (i.e. eco-efficiency) makes good business sense. No employee or manager would ever successfully argue that they should be doing ‘less with more’ (i.e. less output from more resources), or that they should be actively working to create more waste! Waste costs money, is detrimental to the environment and is generally bad for business. The dairy industry has achieved substantial improvements in efficiency over recent years. Yet careful examination still reveals elements of waste — wasted money, wasted resources (such as energy and water) and wasted product. Although eco-efficiency makes good business sense, there are some barriers that limit its uptake. This chapter discusses those barriers and shows how they can be overcome, through a case study that draws on the experience of Murray Goulburn and its involvement in the Commonwealth Government’s Energy Efficiency Best Practice Program — a program that was designed to address internal organisational barriers to change. Although Murray Goulburn’s experience was focused specifically on energy, the approaches that were developed can be used to implement each of the eco-efficiency areas highlighted in this manual.
2.1
Barriers to eco-efficiency ‘The main barrier to the implementation of most projects identified by others is that of ownership of the problem. Support from senior management is also imperative to ensure success of the project.’ — Ted Isaacs, Murray Goulburn Cooperative, Leongatha
In researching this manual we asked staff what they saw as the key barriers to the implementation of eco-efficiency. Their responses included: • lack of capital • lack of time and human resources • operator awareness and training — particularly when there are many casual staff • lack of communication • unsystematic approaches to eco-efficiency initiatives that prevent projects from being implemented, being completed or being reversed at a later time if necessary • getting senior management and board approval for projects. There are no simple answers for these and the many other potential barriers that exist within organisations; however, each of them must be overcome if the eco-efficiency project is to be successful.
MAKING ECO-EFFICIENCY HAPPEN IN YOUR ORGANISATION
13
Here are some of the key points to consider: • Develop management awareness, commitment and support for projects. This is important from the beginning, and throughout projects, to ensure there is time for holding team meetings, performing process trials and implementing solutions. • Establish a cross-functional working group. This should include a range of staff, including cleaners, operators, engineers and managers. • Hold regular team meetings, to keep focus and to ensure continued progress. • Determine baseline information on resource consumption and waste generation. When you achieve savings it is important that you can clearly communicate exactly what those savings are. There must be a clear picture of the situation before the savings were made. • Ensure that you develop good business cases for the eco-efficiency projects that you are trying finance. This should include clearly communicating additional benefits such as positive publicity, improved involvement with the local community, safety, and operational benefits. In some instances you might also explore whether there are alternative approaches that have not been considered. More detailed information on carrying out an eco-efficiency assessment is available in the UNEP Eco-efficiency toolkit for the Queensland food processing industry, which includes a self-assessment guide (UNEP 2004).
2.2
Avenues for supporting the implementation of eco-efficiency One of the most effective means of implementing eco-efficiency is through site-based cross-functional teams. This is discussed further in the next section, in the context of the Murray Goulburn experience. Here are some other ways in which dairy processing companies have supported and implemented eco-efficiency projects: • The appointment of designated managers and supervisors. Many dairy processors have appointed managers to work specifically on projects within the company that improve product yield and reduce waste (e.g. Murray Goulburn’s Process Improvement Manager or Energy Manager).
• Partnerships with suppliers and customers to improve production efficiencies and reduce the use of resources. Some dairy processing companies have formed partnerships with chemical suppliers to optimise clean-in-place systems and reduce chemical use. Partnerships with packaging suppliers have reduced the environmental impacts of packaging, often driven by the National Packaging Covenant. Similarly, partnerships with customers have improved efficiency and reduced waste by solving supply chain management problems.
14
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
• Including eco-efficiency aspects in tender and proposal documents. If it is specified in tender documents that resource consumption must be considered during the design stages of projects, it can go a long way towards improving process yields and reducing environmental impacts. Examples might include the installation of metering devices during commissioning stages, the selection of less resource-intensive equipment, or improved process layout design. • Environmental management systems. If the company has established an environmental management system (EMS), this can also provide an opportunity to integrate eco-efficiency into the way things are done in the organisation. An EMS provides a management structure that allows for setting targets, clarifying responsibilities, training, and raising awareness to achieve environmental improvement. A focus within the EMS on continuous improvement will allow it to be used to go beyond mere compliance and achieve many of the environmental improvement opportunities discussed in this manual. An EMS can also provide legitimacy within an organisation for a focus on eco-efficiency — particularly where the organisation also has an environmental policy that commits it to a high level of environmental performance. • Grants and partnerships with government bodies. There are opportunities to obtain national and state government grants, which can provide encouragement and financial support for improving efficiency through the use of more efficient technology and research. • Support from industry associations. Organisations such as Dairy Australia, the International Dairy Federation (IDF) and the Dairy Processing Engineering Centre (DPEC) provide valuable resources in the form of publications, training and advice that can be used to support an eco-efficiency program. Making eco-efficiency happen within your organisation requires support from a range of areas; it is not the sole responsibility of one particular manager or group. It depends on support and encouragement from all levels of your organisation, as well as external stakeholders such as suppliers, customers, industry associations and government. A good way of getting started is through a site-based team, as described in the next section.
2.3
The Murray Goulburn experience
2.3.1
Building skills, knowledge and support through site-based teams Site-based teams provide an excellent mechanism for breaking down the many barriers to cross-functional communication that limit the uptake of eco-efficiency improvements. They also build a sense of ownership and awareness of environmental issues at the site level. This is demonstrated by the work of Murray Goulburn’s energy team at the company’s Rochester site. The Rochester energy team demonstrated that better energy management saves money, reduces waste and helps build links with the local community.
MAKING ECO-EFFICIENCY HAPPEN IN YOUR ORGANISATION
15
To get a team together, a flyer was put on the Rochester noticeboard, inviting staff involvement. The only requirement was that the team should include a range of staff from different functional areas — operators, maintenance staff, boiler technicians, supervisors and an engineer. The cross-functional make-up of the group was the key to its success. This was demonstrated at the team’s first meeting; when it was exploring potential energy-efficiency projects, the members came up with over 50 different opportunities. Key learning When you can tap into a cross-section of skills and knowledge from different functional areas the possibilities for improvement are much greater. Why? Because everyone gets the opportunity to share their own perspective. This opens up the possibility of identifying and implementing projects that might otherwise be left alone because of the difficulty of working across functional areas. When people identify problems themselves and are given the opportunity to do something about them, they are also more committed to making them happen.
In order to determine which projects they should focus on, the team carried out a number of activities. • It reviewed existing onsite energy data and monitoring equipment. The members knew they first had to understand how energy was used and wasted, in order to understand the potential for savings. • It identified the people who could help or hinder them in implementing their projects (key stakeholders). The members invited their branch manager, a senior engineer and the environmental manager to a meeting, in which they asked questions about the kind of support they could expect for their projects. This group of people also provided valuable input to the technical and organisational aspects of the projects. • It developed a business plan that mapped out the resources required, the likely financial savings and other benefits that would be achieved, and the people and tasks that would ‘make the projects happen’. The business plan was presented to the managing director to get his input, and ultimately his support, for the team’s activities. Key learning In developing the business plan, the team had learnt a lot about their site, its production process, and the opportunities and challenges of implementing change. Their discussions with key managers across the organisation helped develop support from outside the team, and helped them to be very clear about what they needed to do to successfully implement eco-efficiency.
The first project the team implemented was achieved through improved communication between the boiler house and process operators. It did not require any capital outlay but led to annual savings of $180 000 and 1536 tonnes of CO2 (which contributes to global warming). The following different perspectives and the team approach contributed in various ways to identifying and implementing this project:
16
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
Process operator perspective Steam is a critical production input. Any time delay in the provision of steam has a direct impact on production. Steam must be available and ready to go at all times.
Boiler operator perspective Process operators require steam. To ensure that steam is readily available at all times two boilers need to be warmed up and ready to go. Even though it is inefficient to have them idling at 30%, steam must available quickly.
Eco-efficiency perspective Operating boilers at 30% load is inefficient and expensive, and generates greenhouse gas emissions unnecessarily.
Benefits of a team approach Because process operators and boiler operators were both part of a team that had a shared goal and commitment to saving energy, it was obvious to both groups that improved communication would allow the boilers to be run more efficiently, while at the same time ensuring that the process operators were not left without steam when they started up a production process. Because they came up with the idea of the project themselves, there was a lot more commitment to implementation and ensuring that the improved communication processes actually worked.
2.3.2
Raising management awareness of the benefits of eco-efficiency It is critical that both company and site management understand and support eco-efficiency. Following the work of the Rochester team, Murray Goulburn held a special meeting for all senior and site managers to explore the risks and opportunities that energy management held for the business overall. The workshop included: • an update on the scientific and political developments of global warming and climate change, and its likely impact on business • a presentation from representatives of the Rochester energy team, discussing how they achieved $180 000 of energy savings and were on track to achieve more • an interactive session to identify strategies and actions that would support a more focused approach to energy management across all Murray Goulburn sites. After the workshop it was agreed that representatives from each of Murray Goulburn’s seven sites would attend a two-day workshop to discuss and develop action plans for establishing energy management teams on each site. Soon after, a new position of Energy Manager was created, and filled by a senior engineer, to ensure that there was a strong link between corporate and site-based energy initiatives.
MAKING ECO-EFFICIENCY HAPPEN IN YOUR ORGANISATION
17
2.4
Summary There are some barriers to the implementation of eco-efficiency. The best approach to overcoming these barriers will depend on the nature and priority of each organisation, its culture, and working approaches adopted at each site. The keys to successful implementation of eco-efficiency include: • developing management awareness, commitment and support • establishing a site-based cross-functional working group • involving and obtaining the support of external stakeholders such as suppliers, customers, industry associations and perhaps government • reporting back to, and discussing eco-efficiency initiatives at, regular team meetings • establishing baseline information on resource consumption and waste generation • ensuring that good business cases are developed for eco-efficiency projects. Environmental management systems can provide an important framework for eco-efficiency, as they supply a structure for setting targets, clarifying responsibilities, training, and raising awareness to achieve environmental improvement. The work done at Murray Goulburn demonstrates one successful approach to implementing energy efficiency. Consider your own unique circumstances. You can use the ideas presented in this chapter to develop your own implementation plan for eco-efficiency.
18
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
3
Water
3.1
Overview of water use This chapter discusses water use in dairy processing plants. Eco-efficiency opportunities are discussed under the broad categories of reducing demand in processing, cleaning, utilities and amenities, followed by opportunities for recycling and reuse, and finally a brief discussion on wastewater treatment.
3.1.1
Water use in dairy factories The total amount of water used by the dairy industry is approximately 3000 GL/yr, which is equivalent to 13% of Australia’s total freshwater resources (Lunde et al. 2003). Of this, 99% is attributed to on-farm use, indicating that the main opportunities for reducing water consumption in the dairy industry are to be found in improving the efficiency of milk production at the farm. Nevertheless, there are still gains to be made by dairy processors in minimising water consumption within factories. The source and quality of water is an issue for some processors, depending on their location. Generally they use town water, but other sources include river water, irrigation channel water, bore water and reclaimed condensate. Water shortages in both regional and urban areas are leading processors to review the effectiveness of their onsite water use, both of their own accord and in response to pressure from local authorities. Dairy factories also produce high volumes of moderate to high-strength liquid wastes (i.e. with high BOD and COD levels). Water and wastewater management can incur costs for dairy processors, and these vary according to the location of the processing plant, the source of water and the requirements for effluent treatment. The location and type of processing plant and the options for effluent discharge play major roles in determining the level of water reuse and recycling, as well as the degree and method of effluent treatment. Factories in regional areas often have the option of using effluent water for irrigation and may therefore not realise the major financial or environmental benefit to be gained from treating and reusing effluent within the factory. Generally, dairy processors who can reduce water use over the broader system (including upstream and downstream of processing plants), without compromising quality or hygiene standards, will benefit from reduced water supply and effluent charges as well as improving the sustainability of the dairy processing industry. HACCP plans play an important role in ensuring that hygiene standards, which are critical to producing a quality product, are met. Water is used in dairy factories for processing and cleaning, for the operation of utilities such as cooling water and steam production, and for ancillary purposes such as amenities and gardens. Figure 3.1 shows an example of water use in a dairy processing factory that produces market milk.
WATER
19
Figure 3.1
Breakdown of water use of a market milk processor Manual washing 6%
Trade waste 4%
Other 3% CIP 28%
Cooling towers 6% Operational processes 12% Crate wash 16%
Pasteurisation 25%
Many dairy processors track the overall consumption of water by monitoring the ratio of water to raw milk intake. Water consumption in Europe has been reported to range from 0.2 to 11 L/L milk (Daufin et al. 2001) with effluent volumes per raw milk intake in the same range. Ratios for Australian processors producing any combination of white milk, cheese, powders or yoghurts range from 0.07 to 2.90 L/L milk, with the average being around 1.5 L/L milk (UNEP 2004). Table 3.1 shows the range of ratios for factories producing white or flavoured milks, cheese and whey products, and powdered products. For factories that produce powdered products, there is the potential for the majority of water (>95%) to be supplied from treated condensate, also known as ‘cow water’. However, the potential for recovering condensate depends on the scale of a particular powder plant and the ratio of supply to demand on a given day. For example, if the production rate is reduced during the off-peak season there will consequently be less condensate available for recovery. The range in water to milk intake ratios indicates there is potential for some dairy processing plants to decrease water consumption significantly. Table 3.1
Water to milk intake ratios (L/L)
a
3.1.2
Min.
Max.
Average
No. of plants providing data
White and flavoured onlya
1.05
2.21
1.44
7
Cheese and whey products
0.64
2.90
1.64
3
Powdered products
0.07
2.70
1.52
10
Excludes UHT milk.
The true cost of water Water is often viewed as a cheap resource — which is not surprising, considering that Australians pay more for 1 L of milk than for 1000 L of water. Increasingly, however, there is a shift away from this attitude, with an increase in community awareness of the value of water and a trend for local councils and water authorities to move
20
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
towards full cost recovery for the supply of fresh water and treatment of wastewater. Table 3.2 shows the cost of town water supply for a number of regions where there are dairy processing plants. These costs range from 50c/kL for water supplied from the Goulburn Murray Water Board to $1.28/kL for Ipswich City Council. The relatively low cost of water supply in some regions can be a barrier to implementing water conservation projects when payback periods are considered. Table 3.2
Water supply costs in dairy processing regions
a
Council
State
City/town
Water supply cost ($/kL)
Sydney Water
NSW
Penrith
0.94
Hunter Water Corporation
NSW
Hexham
0.85
South Australia Water
SA
Mount Gambier
1.00
Gippsland Water
Vic.
Maffra
0.54
Goulburn Valley Water
Vic.
Tatura
0.47
South West Water Authority
Vic.
Warrnambool
0.58
Eacham Shire Council
Qld
Malanda
0.20a
Brisbane Water
Qld
Brisbane
1.13
Ipswich City Council
Qld
Booval
1.28
Devonport City Council
Tas.
Devonport
0.70
Water supply from river, not town water
The components making up the total true cost of water for dairy processors are: • purchase price • treatment of incoming water • heating or cooling costs • treatment of wastewater • treatment of evaporator condensate for reuse • disposal of wastewater • pumping costs • maintenance costs (e.g. pumps and replacement of corroded pipework and equipment) • capital depreciation costs. Table 3.3 provides an example of the full cost of ambient and hot water. It indicates that, while the purchase cost of the water was $0.54/kL, the true cost was actually $2.33/kL for water at ambient temperature and $5.13/kL for hot water. The cost of wastewater discharge in different regions is discussed more fully in Chapter 5, ‘Yield optimisation and product recovery’.
WATER
21
Table 3.3
3.1.3
Example of the true cost of ambient and hot water ($/kL) Purchase
$0.54
Wastewater treatmenta
$0.75
Wastewater pumping
$0.05
Wastewater discharge (volume charge)
$1.09
True cost of ambient water
$2.43
Heating to 80°Cb
$2.80
True cost of hot water
$5.23
a
Based on assumption of treatment costs for an anaerobic digester
b
Cost for heating to 80°C using steam produced by a gas boiler
Measuring water consumption To understand how to manage water effectively it is essential to understand how much water enters and leaves the factory and where it is being used. Understanding water flows will help to highlight where the greatest opportunities for cost savings are. This can be achieved by developing a detailed water model for the site using dedicated software or a simple spreadsheet. The water model should balance the total water entering the factory over a period with the volume of water used in processing and finally disposed as effluent. There are a number of methods that can help to quantify water use and develop a water model: • Install flow meters in strategic areas to directly measure water use. • Use a bucket and stopwatch to estimate flow from pipes or hoses. • Use manufacturers’ data to estimate water use for some equipment and compare with actual water use. • Use known operational data to estimate water use (e.g. a 10 kL tank fills every wash cycle). When identifying areas of water use, manual operations as well as equipment should be monitored carefully (e.g. the volume of water used for washing down floors and equipment must be taken into account). It is also a good opportunity to observe staff behaviour (e.g. taps left running or hoses left unattended).
Flow meters Flow meters on equipment with high water consumption, incoming water inlets and wastewater discharge outlets will allow regular recording and monitoring of water use. Flow meters are also useful for measuring ‘standing still’ water consumption during periods when equipment is not operating, to detect any leaks. When installing a meter ensure that the meter is tailored to meet the application (e.g. measurement of product wastewater or clean-in-place volumes).The cost of installing or hiring flow meters will vary according to the meter size and functionality. Factors to consider include pipe size,
22
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
flow rate (L/min), fluid quality (e.g. incoming potable water, wastewater, process water), type of power supply (mains, battery or solar), accuracy required and piping installation costs. It is also particularly important to consider ongoing maintenance and recalibration costs. Often a higher capital cost with lower maintenance costs can result in lower life-cycle costs. ‘Every Drop Counts’ Improved water management: Dairy Farmers, Lidcombe Dairy Farmers in Lidcombe joined the Sydney Water ‘Every Drop Counts’ water minimisation business partnership. The company installed 27 water meters across the site and worked on developing an accurate understanding of water flow to each area. A water assessment was undertaken over a number of months, identifying savings by preventing cooling tower overflow; recirculating homogeniser water, crate wash water and DAF water; reducing water for cleaning; repairing leaks; and reviewing truck washing practices. The assessment identified total savings in water costs of $300 000/yr with an initial cost of $150 000 and ongoing costs of $26 000/yr. Improved water management: National Foods, Penrith National Foods Ltd in Penrith also joined the Every Drop Counts partnership. Additional water meters were installed and these were fitted with pulse unit and data loggers, allowing the daily water usage to be recorded and downloaded to a central system. Water usage for the site was mapped and potential improvements identified, including redesign of the crate wash system, improved maintenance and monitoring, more efficient pasteuriser and bottle washing, collection of rainwater, and reductions in water use for pump seals. Water use for the site was reduced by 22% as a result of the program, reducing water use by 110 kL/day and saving $104 000/yr, with implementation costs of $86 000.
3.1.4
Increasing staff awareness and involvement The involvement and support of staff is essential in reducing water use. Ideas for involving staff and encouraging water conservation include: • forming a water management team • using posters and stickers to promote awareness of water efficiency • implementing staff suggestion schemes to encourage ideas for reducing water use • promoting progress by displaying graphs and performance measures • regularly discussing water efficiency at staff meetings • considering a staff incentive scheme and including targets in staff job goals. Involvement of staff, the establishment of clear goals and targets, and prompt implementation of initiatives can help develop a strong water conservation culture. ‘It is important to set targets and allow operators active involvement in developing improvements.’ — Adam Carty, Murray Goulburn Cooperative, Kiewa, Victoria, commenting on minimising site water use.
‘One of the main issues is operator awareness and training. With such a large number of casual and seasonal staff, training and awareness has to be maintained so that eco-efficient projects are continually generated from the floor and maintained.’ — Peter McDonald, Murray Goulburn Cooperative Co., Koroit, Victoria.
WATER
23
Increasing staff awareness: Murray Goulburn Murray Goulburn Cooperative sites introduced environmental awareness training into their staff inductions. The inductions have a ‘two-tiered’ approach where staff have a training session which is followed up a few months later to reinforce the earlier message. This has ensured that all staff are aware of the initiatives to minimise water use and are encouraged to generate projects. Measurement of resources: Peters and Brownes, Balcatta Peters and Brownes in Balcatta have built a site database of utility usage/production data, which provides ‘year to date’ usage of electricity, gas and water consumption. Water, electricity and gas usage is metered within strategic locations of the factory allowing resource use to be analysed by area, and the information is available to managers online.
3.2
Reducing demand for water: processing
3.2.1
Optimising rate of water flow Sometimes equipment operates at water pressures or flow rates that are variable and set higher than necessary (e.g. pump sealing water, homogeniser cooling water, belt filter sprays or carton machine cooling water). By conducting trials to determine the optimum flow for the equipment or comparing the flow rate with manufacturers’ specifications, consumption could be reduced. To maintain a constant and optimum flow rate, consider installing a flow regulator. Optimising homogeniser cooling water: Dairy Farmers, Mount Gambier Dairy Farmers in Mount Gambier reduced water costs by $10 800/yr, by reducing the flow of cooling water to the homogeniser to the optimum rate. The cost was only $250 for the installation of a flow regulation valve.
3.2.2
Efficient process control Installing automatic monitoring and control devices in key sites can lower production costs. A wide variety of devices are used in dairy factories to detect operating parameters such as level, flow, temperature, pH, conductivity and turbidity. These are particularly important for detecting the quality of processing and waste streams to enable the maximum recovery of product, chemical and water. Refer to the DRDC publication Milk processing effluent stream characterisation and utilisation (DRDC 1999) for information on instrumentation and methods for monitoring and controlling waste streams. Water sprays are often used in dairy factories for washing, or to lubricate equipment. Water is wasted if sprays are left operating unnecessarily during breaks in production; this can be prevented by linking sprays to conveyor or equipment motors, using automatic cut-off valves. Timers may also be useful for shutting off sprays or taps when not in use.
24
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
3.2.3
Leaks Leaking equipment such as pumps, valves and hoses should be promptly repaired, not only to save water, but also to set a good example to staff on the importance of water conservation and good housekeeping. Equipment that is left leaking over lengthy periods can waste significant amounts of water or product. Table 3.4 gives some examples of the cost of water loss from leaking equipment. For equipment items that use large volumes of water, the cost of installing and regularly monitoring meters to detect leaks can be well justified. If possible, it is a good idea to take supply water meter readings during non-production hours to highlight any unusual water consumption or even leaking pipes. A system for reporting and promptly repairing leaks should also be established.
Taking supply water meter readings during non-production hours can highlight any unusual water consumption or leaking pipes.
Table 3.4
Cost of water loss from leaking equipment Equipment
Hourly loss (L)
Annual loss (kL)
Water cost ($/yr)
0.5
5
12
6
53
128
0-240
0–2100
0-5103
Ball valve (7–14 L/min)
420–840
3680–7360
8 942–17 885
1-inch hose (30–66 L/min)
1800–4000
15 770–34 690
38 321–84 297
Union/flange (1 drop/s) Valve (0.1 L/min) Pump shaft seal (0–4 L/min)
Assumptions: purchase cost of water = $0.54/kL; total cost of water = $2.43/kL (see section 3.1.2) Table derived from hourly and annual water loss figures in Envirowise 2003.
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25
3.3
Reducing demand for water: cleaning A large proportion of the water consumed by dairy processors (50–90%) is used for cleaning equipment and surrounding areas of the plant (Envirowise 1999a). There are numerous opportunities for reducing water use for cleaning, as outlined in the following section. The Dairy Process Engineering Centre (DPEC) publication Performance evaluation guide manual — cleaning systems 98/99 (DPEC 1989/99) is a practical guide for evaluating the effectiveness of a cleaning system and benchmarking current performance. It also includes a worked example and ready-to-use work sheets. Another useful resource is CIP: cleaning in place (Romney 1990).
3.3.1
Design and selection of processing equipment and process layout Criteria for the selection of equipment and the design of process layout should include ease of cleaning. This will minimise the risk of product contamination and spoilage, as well as reducing water and chemical use and the time taken for cleaning. Pipe runs should be designed with minimal bends and dead legs where contamination can occur. Additional valves may be installed in existing pipes to prevent them from acting as dead legs; and pipes should run on a decline to allow for efficient drainage. Floor surfaces should be designed to promote run-off, to reduce the need for hosing of product residues.
3.3.2
Dry cleaning Dry cleaning not only reduces water and chemical use but also reduces the volume of wastewater and improves its quality. As much product as possible should therefore be removed from plant and equipment by dry cleaning techniques before being washed down. In some cases usable product can be recovered also. Cleaning aids such as squeegees and brushes are used in dairy factories, and care must be taken to ensure they do not become a source of contamination. For this reason, some factories use distinguishing features such as colour coding so that cleaning aids are used only in designated areas. Scrubber dryers and vacuum cleaners can wet or dry clean and remove gross soiling before washing with water to reduce the amount of wastewater that would normally be discharged to the drain. They are fast and efficient, reduce chemical use, and are suitable for relatively dry areas such as cold stores or warehouses where hosing is unsuitable and there may be large expanses of floor space.
3.3.3
Trigger-operated controls for hoses Hoses left on unnecessarily waste water. For example, a hose left unattended for a total of one hour each day can lose between 470 kL and 940 kL annually, equating to $1000–$2000 every year for each hose.1 The cost of a trigger gun can range between $20 and $200 for a heavy-duty unit.
1
26
Assumptions: $2.43/kL for true water cost; 260 days each year; hose flow rate of 0.5–1.0 L/s
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
A hose left unattended for a total of an hour a day can waste as much as $1000–$2000/yr.
Reuse of pasteuriser water, and hose water-saving devices: Parmalat, Nambour Parmalat in Nambour previously sent pasteuriser cleaning water to wastewater. Storage tanks and pipework have now been installed to allow the water to be reused for washing empty milk crates. In addition, water-saving devices have been attached to hoses used for cleaning. This has saved the company 1 kL of water per shift or 260 kL/yr.
3.3.4
High-pressure cleaning systems High-pressure water cleaners are typically used to clean floors and some equipment. They can use up to 60% less water than hoses attached to the water main (Envirowise 1998). Mobile high-pressure cleaners can have flow rates ranging from 4 L/min to 20 L/min and pressures of up to 500 kPa. In a dairy processing plant, high-pressure cleaners may be useful for cleaning areas such as around wastewater treatment plants, cooling towers and some floor areas. They may not be useful around some processing areas due to the possibility of creating aerosols.
3.3.5
Clean-in-place systems Clean-in-place (CIP) systems are commonly used in dairy processing plants for cleaning tanks, piping, filling machines, pasteurisers, homogenisers and other items of equipment. A well-designed system minimises the use of water and chemicals; it also saves the labour required for manual cleaning. The most eco-efficient CIP systems are multi-use, where rinse water and chemicals are recovered and stored for reuse. Chemicals and water used in some CIP systems are recovered using membrane filtration.
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In most systems, interfaces between product, chemical and rinse water are detected using conductivity or turbidity meters; other systems use timers. The effectiveness of conductivity and turbidity meters compared with timers is a topic of debate. Timers may not provide a consistent or repeatable quality of clean due to factors such as varying flow rates, pressures, and pump or valve wear; meters can fail, causing operating delays or unnecessary loss of product, chemicals or water to the waste stream. In addition, instrumentation can ‘drift’ out of calibration over time; and timers can be adjusted to compensate for operational factors. Regardless of which system is used, it is important to regularly verify chemical strengths and temperatures as well as carrying out visual checks, if possible, to ensure equipment is clean. These checks may be done every day, shift or clean. It is also important to carry out longer-term monitoring — for example, every 12 months to validate CIP system settings and review timers, chemical concentrations, temperatures and general cleaning effectiveness. For further reading on CIP systems see AS 1162:2000, Cleaning and Sanitizing Dairy Factory Equipment; and AS/NZS 2541:1998, Guide to the Cleaning-in-Place of Dairy Factory Equipment. CIP systems are also discussed further in Chapter 7, ‘Chemical use’, which includes information on types of chemicals used and typical concentrations. ‘When optimising CIP systems, take one step at a time and don’t try to make too many changes at once.’ — Alison Dilger, National Foods, Morwell Reuse of water by CIP system: Pauls Ltd, Stuart Park1 Pauls in Stuart Park previously utilised a single-use CIP system where all water and chemicals were used once and then discharged to waste. The system has been replaced with a multi-use CIP system that recycles final rinse water for the pre-rinse cycle. All chemicals used in the system are also returned and circulated through holding vats, where temperature and conductivity are monitored and automatically adjusted to meet specifications. The new CIP system saves Pauls $40 000/yr, with a payback period of only one year. Fine-tuning of CIP system: National Foods Ltd, Penrith National Foods in Penrith, as part of a regular audit of CIP systems, reviewed the flush time of their pasteuriser. They were able to reduce the flush time by 12 min/day, which resulted in water savings of 15 ML/yr. Validation of CIP System: National Foods Ltd, Morwell During the early stages of commissioning the National Foods Morwell plant, there were problems with product quality and cleaning times, and concentrations of cleaning agents were increased. As the quality issues were resolved it was found that many concentrations and times were above recommended levels. These were able to be reduced without compromising product quality, although there were challenges in convincing others that this was the case. The costs of implementing the changes were just the time and tests required to make the changes. Savings were in the order of $100 000 /yr. Upgrade of major CIP set: Murray Goulburn Cooperative, Koroit Murray Goulburn’s Koroit factory upgraded its CIP system and installed additional tanks for the storage of used and clean caustic. Previously, not all the evaporators had access to the CIP system, so water and chemicals were disposed after a single use. The initiative ensured increased chemical recovery, better quality of chemical supply, reduced effluent volume and less plant downtime; it led to savings of $80 000/yr. The cost of implementation was $90 000. Optimisation of CIP system: Murray Goulburn, Leitchville Murray Goulburn in Leitchville incorporated its milk pasteuriser CIP system into the cheese room CIP system, allowing water and chemicals to be reused rather than being sent to drain after a single use. The project outlay was $50 00, with savings of $73 000/yr in chemicals and 16 kL/day of hot water. 1
28
Environment Australia 2001
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
CIP rinse recovery: Bonlac Foods Ltd, Spreyton At Bonlac Foods in Spreyton large volumes of water are required for final rinsing after CIP of the separators and evaporator. After the chemical concentration has dropped to an acceptable level this water is diverted from the wastewater system to an irrigation dam. Excessive chemical contamination of irrigation water is avoided by the use of conductivity probes.
Burst rinsing Burst rinsing is becoming more commonly used for the pre-cleaning of tanks and tankers to maximise product recovery before CIP. Depending on the characteristics of the product being cleaned (e.g. its viscosity), a series of bursts rather than a continuous rinse can minimise water use. One disadvantage is that it can add time to a cleaning cycle.
Burst rinsing of tankers: Murray Goulburn, Leongatha Murray Goulburn in Leongatha routinely rinsed its milk tankers before CIP, flushing out the milk solids and losing them to effluent. Burst rinsing, which has now been introduced, displaces milk solids from the tanker and associated lines without excessive dilution. The milk solids are recovered for processing. Burst rinsing: Peters and Brownes, Balcatta Peters and Brownes in Balcatta introduced burst rinsing into the ice-cream CIP after an audit by the factory’s chemical suppliers. The initiative required some small program changes to the CIP automation system but resulted in water savings of 15 ML/yr or $20 000. The plant found burst rinsing could not be used for all operations; for example, it added too much time to the cheese processing cleaning cycle where time was critical. Also, burst rinsing was not continued in areas of the beverage plant because there were no savings. The plant is continuing trials in other areas.
Spray balls and nozzles Spray balls and nozzles are an integral part of a CIP system. Spray nozzles for tank cleaning usually come in three main types: • fluid-driven tank wash nozzles which are rotated by the reactionary force of the fluid leaving the nozzle • motor-driven tank washers, controlled by air or electric motors which rotate the spray head for high-impact cleaning • stationary tank wash nozzles or spray balls which use a cluster of nozzles in a fixed position. Spray balls and nozzles should be selected to suit the application, particularly with regard to the temperature and corrosive nature of the cleaning fluids. Spray nozzles should be regularly monitored and maintained and their efficiency reviewed as part of a cleaning validation program.
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Water-efficient spray nozzles: milk and beverage processor, USA Schroeder Milk Co. in Minnesota now saves around 20 000 L daily after improving the efficiency of spray nozzles on its carton washer. The company changed from using shower heads and spray bars to smaller nozzles and mist sprays, and now only operates the washer when needed instead of continuously.1 1
3.3.6
University of Minnesota 2003
Scheduling or modifying product changeovers Efficient product scheduling and planning of product changeovers is an effective means of reducing resource consumption for cleaning and is commonly practised by dairy plant managers. Product changeovers should be optimised so that equipment cleaning is kept to a minimum and productivity is maximised.
‘Pigging’ systems Pigging is a method of removing product from pipes; it can reduce the volume of water required for cleaning by minimising residual product left in the system, and therefore reduce rinse times. Pigging systems are discussed further in Chapter 5, ‘Yield optimisation and product recovery’. Effluent volume prediction model: Murray Goulburn, Leongatha Murray Goulburn in Leongatha uses an Excel-based effluent volume prediction model to monitor and help schedule CIP washes. The model is used to prevent the wastewater system from being overloaded and allows wastewater volumes to be benchmarked and potentially reduced.
3.3.7
Crate washers Crate washers can use a significant volume of water in a plant producing short shelf-life milk. The breakdown of water consumption in Figure 3.1 shows crate washing as accounting for 16% of the total water used. Crate washers can be prone to leaks and it is important that they are well maintained. Recirculating water in crate washers is a relatively easy method of reducing consumption. Another idea is to investigate adjusting the washer speed and length of cleaning cycles, to achieve the most efficient clean while still meeting hygiene standards. Redesign of crate wash system: National Foods Ltd, Penrith National Foods in Penrith redesigned its crate wash system to allow the recirculation of water. The improvement saved 60 kL/day of water and $105 000/yr, based on water supply and discharge costs. The cost of implementation was $50 000.
30
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
3.4
Reducing demand for water: utilities
3.4.1
Blowdown in cooling towers and boilers Blowdown prevents the build-up of dissolved solids deposits in cooling towers and boilers, which reduces operating efficiency. Cooling towers and boilers often operate with a constant blowdown flow, or are timed to release water at regular intervals while some blowdown is regulated manually. In order to minimise the flow of make-up water needed after each blowdown, a conductivity probe can be installed. The probe initiates blowdown only when the conductivity in the water exceeds a set value. It may be possible to reuse boiler blowdown water for non-product uses such as floor cleaning or perhaps ash sluicing (for factories with coal-fired boilers). Blowdown can also be a good source of recovered heat, as discussed in Chapter 4, ‘Energy’.
3.4.2
Cooling tower operation Cooling towers can be a source of microbial contamination, or can use excessive water, if they are not well maintained. A regular maintenance schedule will enhance the tower’s efficiency and maximise its lifespan. Requirements for microbial control measures are set out in AS/NZS 3666.1:2002, Air-Handling and Water Systems of Buildings — Microbial Control — Design, Installation And Commissioning, and in guidelines issued by state health departments. Float valves are used on many cooling towers to control make-up water supply. The valve should be located in a position where it cannot be affected by water movement as a result of wind or water flowing through inlet pipes into the tower basin.
Cooling towers should be regularly checked for leaks and scale build-up.
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Overflow of water on cooling tower: Murray Goulburn, Leongatha Murray Goulburn in Leongatha conducted a water audit, which identified that one of the cooling towers was intermittently overflowing. The leak was measured at 120 L/min, which equated to around 57 000 L/day, assuming the leak occurred 30% of the time.
3.4.3
Equipment sealing water Some items of equipment, such as vacuum pumps, centrifugal pumps and homogenisers, require sealing and cooling water. Often this water is used ‘once through’ and disposed to drain after a single use. There can be opportunity for substantial savings by recovering this water for other uses. In the case of pumps, an alternative is to use types that have a dry mechanical seal; however, care must be taken if using dry seals for pasteurised products, due to the possible risk of contamination if product reaches past the seal and cannot be easily removed during cleaning. Recirculation of vacuum pump sealing water: Murray Goulburn, Koroit Murray Goulburn Cooperative in Koroit installed a water recirculation system on the powder packing plant vacuum pumps, reducing water use by approximately 10 000 kL/yr and saving $5000 in water supply costs. Wastewater at Koroit is used for irrigation, so there were no additional savings in disposal costs. Recirculation of vacuum pump sealing water: Murray Goulburn, Leitchville At the Murray Goulburn Leitchville factory a water recirculation system was installed on the vacuum pump. The water is cooled using an air-cooled radiator. The project was very successful, saving $27 000 in maintenance costs and 1.1 million L/yr in water that was previously sent to drain. The cost of implementation was $15 000, which included a pump, balance tank, pipework and fan. Recirculation of homogeniser water: Dairy Farmers, Bomaderry At Dairy Farmers in Bomaderry most of the pumps and homogenisers require water cooling for their seals. Where possible, recaptured condensate water is used on the pump seals. There are three homogenisers on the site, all of which are now fitted with water recycling units; these recycle water used on the homogeniser seals and only require dumping and cleaning once a day. Now around 15 kL of water per day is saved, with mains water costs of $120/day. The cost of the recirculation system was approximately $4500.
3.5
Ancillary water use Water use in amenities, kitchens/cafeterias and gardens may be a small percentage of a factory’s overall water use but there can still be significant savings to be made. Practising water conservation, often by implementing simple and low-cost measures, also sends a strong message to staff. Table 3.5 shows water efficiency ratings and corresponding flow rates of various appliances. A comparison of water-efficient products and non-rated products is shown in Table 3.6, with an indication of potential savings in water volume.
32
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
Table 3.5
Water appliance ratings Rating
Level of water
Flow rates for efficiency (L/min)
Flow rates for basin taps (L/min)
Flow rates for showers (L/place setting)
Flow rates for dishwashers toilets L (average flush volume)
Moderate
6.0–7.5
12.0–15.0
2.0–2.8
5.5–6.5
AA
Good
4.5–6.0
9.0–12.0
1.5–2.0
4.0–5.5
AAA
High
3.0–4.5
7.5–9.0
1.0–1.5
3.5 -4.0
AAAA
Very high
2.0–3.0
6.0–7.5
0.8–1.0
2.5–3.5
AAAAA
Excellent
Not more than 2.0 with automatic shut-off
Not more than 6.0
Not more than 0.8
Not more than 2.5
A
Source: AS/NZS 6400:2003, Water Efficient Products — Rating and Labelling
Table 3.6
3.6
Comparison of water-efficient products with non-rated products Product
Savings
Taps
Non-efficient taps can use more 12 L/min Efficient AAA-rated taps or taps with a restrictor use only 6 L/min
Shower heads
Non-efficient shower heads can use more than 20 L/min High-efficiency roses can use less than 9 L/min
Toilets
Non-efficient toilets can use 12 L of water per flush High-efficiency dual-flush toilets use 3.6 L per flush (based on 4 half flushes to 1 full flush)
Clothes washers
Non-efficient washers can use more than 36 L per kg of washing Efficient front-loading washers can use less than 9 L per kg of washing
Dishwashers
Non-efficient dishwashers can use more than 3 L per setting (14 place-setting dishwasher) Efficient washers can use less than 1 L per setting
Urinals
Non-efficient cyclic flushing urinals are 30–80% less efficient than demand flushing urinals
Stormwater There is potential for dairy processors to supplement water supply through the collection and reuse of stormwater. Stormwater can feasibly be used for non-potable applications in external areas of the processing plant (e.g. pump seal water, floor cleaning, irrigation, garden watering).
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Use of stormwater: National Foods Ltd, Penrith National Foods in Penrith reconnected an existing stormwater collection tank. The stormwater supplements trade waste vacuum pump sealing water, which is also recirculated. The initiative has saved the company 12 kL/day and $4000 in water supply and discharge costs. The initial cost was $2000, with operating costs of $100/yr.
3.7
Water recycling and reuse Some wastewater streams are relatively clean and can be recycled or reused onsite. If the quality of wastewater streams is not suitable, some form of treatment may be necessary if the water is to be reused. In some cases in may be necessary to segregate wastewater systems to allow for reuse. Generally, water that will be in contact with product must be of drinking water quality and meet the Australian Drinking Water Guidelines (NHMRC & ARMCANZ 1996). Water that is recovered for use as boiler and cooling tower make-up must also generally be of high quality, as excessive organics or salts in the water will become concentrated and cause damage through excessive scaling or corrosion. Conductivity is usually used as an indicator of boiler feed-water quality and a maximum acceptable conductivity of 25 µS/cm has been cited (IDF 1988). Advice on the quality of water that can be reused in boilers and cooling towers should be sought from relevant experts. Reuse of pasteuriser flush water: National Foods Ltd, Chelsea Heights National Foods in Chelsea Heights reduced water use by 3 kL/day by recovering water from the pasteuriser flush. Estimated savings per year are greater than 1 ML. The company is planning to implement the same initiative on the remaining pasteurisers. Reuse of pasteuriser sanitiser water: Murray Goulburn, Leitchville Murray Goulburn in Leitchville now recovers pasteuriser sanitising water by returning it to the hot water system. The factory collects around 8 kL of 85°C water per day, which was previously sent to drain, saving around 2900 kL/yr and approximately $1000 in water supply costs. Water from the factory is used for irrigation so there were no savings in disposal costs. The cost of installation was $8000 for a double butterfly valve, non-return valve, pipework and programming. The conductivity sensor and divert valve is used to divert water that may be contaminated. Reuse of instrument cleaning water: Dairy Farmers, Malanda Dairy Farmers in Malanda reuse water used for cleaning inline instruments that are used for testing quality parameters of incoming water such as turbidity. The instruments need to have a constant flow of water across them. The water is stored and pumped back into the water treatment (clarifier) system, saving 26 ML/yr and $5200 per year in water supply costs (based on a cost of 0.20c/kL).
3.7.1
Condensate recovery Condensate water can be generated from two areas in dairy processing plants: from drying and evaporation processes used to concentrate milk products or produce powders (vapour condensate); and from boiler and steam supply systems. Recovery of condensate from these areas is discussed below.
34
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
Drying and evaporation processes Condensate recovery systems are widely used in Australian dairy factories and can provide a substantial proportion of total water supplies. Around 87% of raw milk is water, the majority of which (about 85%) may be recovered, to potentially provide up to 100% of total factory requirements. The benefits of condensate recovery can be twofold, with savings in water consumption as well as in the recovery of heat energy. Vapour condensate, also known as ‘cow water’, can be used in numerous areas of the plant such as boiler and cooling tower feed water, CIP systems, cheese curd wash water, dryer wet scrubbers, indirect heating (via heat exchange) and pump seal water. There are, however, some factors to take into consideration in using condensate: • It may contain carryover of product. • It may require cooling. • It is very low in dissolved solids (measured by conductivity), which can cause corrosion. • It can be odorous. The quality of vapour condensate depends on the type of product that is being evaporated, the evaporator installation, the place of extraction, the efficiency of operating personnel and the care they take. For example, it has been shown that the BOD of vapour condensate produced from concentrating acid whey has been almost 14 times that of condensate produced from concentrating skim milk, which can limit the opportunities for reuse: ‘In general it has been found that the condensate from the earlier stages (effects) of an evaporator can be used after monitoring as boiler feed water, with that from the later stages being suitable for washing floors and the exterior of plant and vehicles.’ (IDF 1988) Generally, without further treatment condensate is classified as non-potable. The IDF Bulletin 232 (IDF 1988) lists a number of requirements for the reuse of condensate: • Stable evaporation operation is the most important prerequisite for obtaining a high-quality condensate. • Continuous inspection and monitoring of the condensate quality is necessary. This is usually done using conductivity and/or turbidity. • It must be possible to chemically clean all the systems used to collect and convey the condensate. • Continuous supervision of the evaporation installation and treatment of vapour condensate is important. • Mixing of condensate with other types of water must be avoided, due to the potential for rapid bacterial growth. • If disinfection is required, condensate should be adequately and properly dosed with disinfectant, with time allowed for additives to react.
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To utilise the maximum available volume of condensate — and depending on the initial quality — further treatment may be needed before use. Methods used for treating condensate include the addition of disinfectants such as silver ions, chlorine and chlorine compounds, and P3-oxonia, as well as technologies such as carbon filtration and ion exchange (IDF 1988). Reverse osmosis is used as a higher level of treatment, to remove unwanted components and produce water that can be reused in most areas of a dairy processing plant. This is discussed further in the next section. Condensate is also often acidic, and may require caustic addition to increase the pH — for example to prevent boiler corrosion if used as boiler feed water. It has been found that the use of relatively clean condensate for cooling tower make-up water can allow the growth of bacteria despite the use of biocides. This can be explained by the relatively low conductivity of the condensate compared to town water, and its effect on the frequency of boiler and cooling tower blowdown. As blowdown is usually controlled on the basis of conductivity, the low conductivity of condensate leads to less frequent blowdown and higher concentrations of organics, which can encourage microbial growth. This can also increase the level of scaling and build-up in the boiler or cooling tower, decreasing the life of the equipment. Condensate is a good source of heat energy, and should be utilised. Significant savings in heating costs can be realised by recovering the heat energy for purposes such as pre-heating product or boiler feed water. For best results, condensate recovery should be integrated into the process at design stage to gain maximum economic benefit from energy and water recovery. Further information can be found in Chapter 4, ‘Energy’. For further reading see the IDF Bulletin No. 232/1988, The quality, treatment and use of condensate and reverse osmosis permeates (IDF 1998).
Boiler condensate return systems Water produced from the boiler system in the form of steam condensate should also be recovered wherever possible, to reduce the amount of make-up water required by the boiler. Reducing condensate loss can reduce water supply, chemical use and operating costs by up to 70% (FEMP 2003). A condensate return system also reduces energy costs, because the already hot condensate requires less energy to reheat. Steam traps, condensate pumps and lines should be routinely inspected, while boiler systems should be maintained to reduce blowdown and maintain boiler efficiency. More information on boiler condensate return systems can be found in Chapter 4. ‘In sensitive areas of the plant, it was necessary to only use recaptured condensate which has a low or no bacterial load.’ — Peter Ryan, Dairy Farmers, Bomaderry
‘We have an EPA licence to send excess evaporator condensate water to the Hunter River. The odour prevents us from using it in the boilers and other products. We have capital works in progress that will enable us to use all of the condensate water that we produce.’ — Garry Christie, Dairy Farmers, Hexham
36
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
Challenges with recovery of condensate water: Bonlac, Spreyton Bonlac at Spreyton recovers milk evaporator condensate, which is cooled before being sent to process water tanks with mains water make-up. The water is sanitised by dosing and recirculating with chlorine dioxide. Whey permeate evaporator condensate is recovered hot and used to supplement boiler feedwater or hot water, or is sent to irrigation. The trace organics in milk condensate rule out its use in some product contact applications. It was also found that acidity of recovered condensate plus excess acid from chlorine dioxide dosing has caused corrosion problems in non-stainless steel piping and equipment. It is important to specify corrosion-resistant piping material and provide for pH adjustment. Recovery of condensate water: Murray Goulburn Cooperative, Koroit Murray Goulburn at Koroit installed a 1 million litre condensate water recovery tank and automated the water recovery system. The installation has increased water-holding capacity and reduced production downtime, due to having immediate access to a bulk supply of water as opposed to waiting for town water. Downtime was also reduced as one of two condensate tanks could be cleaned without shutting down the plant. Savings were approximately 88 000 kL/yr and $50 000/yr for an outlay of $200 000. Over 90% of water requirements are now supplied by the condensate water. One issue with installation was setting up an appropriate water treatment system to ensure the quality of the water. Reuse of condensate water: Murray Goulburn, Rochester Murray Goulburn’s Rochester site recovers 190 ML/yr of condensate from the factory’s milk and whey powder evaporators for use within the plant. Condensate cannot be recovered from all the evaporators due to occasional product carryover. There are also issues with the low pH of some condensate, which precipitates protein and leads to the growth of thermophilic bacteria. Condensate water is blended with town water which is then chlorinated, filtered to remove chlorine, and passed through an ion exchange bed to remove hardness before use. Reuse of dryer condensate water: Murray Goulburn, Maffra Murray Goulburn in Maffra introduced a water recovery and reuse program. Initiatives included using condensate water from dryer air heaters for supplementing boiler and de-aerator feed water; dryer wet scrubbers; indirect cooling in heat exchangers; pump seal water; and external tanker CIP rinsing. Some of the condensate is treated with chlorine dioxide and filtered before reuse. CIP final rinse water is also recovered and used for the first rinse on the next CIP. As a result, fresh water consumption for the factory has reduced by 110 ML/yr and supplementary supplies of town water no longer need to be brought in by tanker. The program has saved the company at least $59 000/yr in water costs, not including tanker transport costs. Condensate recovery, Dairy Farmers: Bomaderry Dairy Farmers in Bomaderry are installing additional storage capacity to allow the collection of 60 kL of condensate water per day. Currently 30 kL water of nearly distilled quality is sent to the boiler for feed make-up. The rest of the condensate will be used as make-up water in the operation of the crate washer. Savings in water costs are expected to be approximately $12 000/yr. Additional savings, which could be high as $25 000, will be made from reduced costs to irrigate and dispose of water. Potential problems with using the water are the volatile organic odours and the small amount of dissolved salts coming off the wash cycles of the evaporator. Discontinued use of condensate for cooling tower make-up: Bonlac, Spreyton Bonlac in Spreyton previously recovered evaporator condensate for use as cooling tower make-up. The low conductivity of the condensate meant that blowdown was less frequent and traces of organics became more concentrated. Persistent contamination of the cooling tower led to the decision to discontinue using condensate for cooling tower make-up.
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3.7.2
Use of membranes for water recovery Membranes are commonly used within the dairy industry for the recovery of product, chemicals or water. This section looks at the use of membranes to recover and reduce the consumption of water. The use of membranes in dairy processing plants is covered further in Chapter 5, ‘Yield optimisation and product recovery’. Some dairy processing plants use reverse osmosis (RO) to polish evaporator condensate. The filtration process removes trace elements, which can cause corrosion. It also removes traces of product (from carryover), thus improving the quality of the permeate and increasing the possibilities for reuse within the plant. Permeate produced from membrane filtration can be used to supplement process water that is in contact with product; however, it requires further treatment to make it potable quality and is more commonly used for boiler and cooling tower water make-up. RO will not remove all the BOD from the stream, but a 90–95% reduction is normally achieved (PCI-memtech 2000). A barrier to the use of membrane filtration for treating condensate water for reuse is the cost of treatment compared with the cost of using fresh town water. For example, it is estimated that the cost of treatment for one Victorian plant is around 90c/kL, whereas the cost of town water is only 69 c/kL (Matthew McGuiness 2004, pers. comm.). Membrane filtration is not suitable for recovering water from all waste streams. For example, water recovered from whey permeates by reverse osmosis should not be used in cheese factories because of the risk of bacteriophage, a virus that disrupts the cell membranes of bacteria used in the cheese-making process (Peter Gross 2004, pers. comm.). Bacteriophage infection can reduce the rate of fermentation in cheese-making and lead to lower-quality cheese. Water recovery using membranes: Murray Goulburn, Rochester Murray Goulburn’s Rochester plant processes around 800 kL/day of whey to produce whey powder and lactose powder. Whey is processed in ultrafiltration, nanofiltration and reverse osmosis plants. The permeate from the RO plant is recycled to the factory as usable water. Over a year the RO plant saves 70 000 kL ($32 000) in reduced water intake. Challenges with RO permeate chlorinator: Murray Goulburn, Leitchville At Murray Goulburn in Leitchville reverse osmosis (RO) permeate is chlorinated before being used to supplement cooling tower and boiler water requirements. The reuse of the permeate allowed mains water use to be reduced by 17%; however, the system had to be shut down due to fouling problems with the membranes, which affected the quality of the permeate. The initial cost of the system was $40 000, with a 12-month payback period. The chlorination system is sized to treat 1 million litres of water per day. Challenges include the amount of chlorination required and control of bacteria in the cooling towers. Novel use of reverse osmosis water: Dairy Farmers, Malanda Whey proteins are processed in a reverse osmosis plant at Dairy Farmers in Malanda. The company installed pipework to allow water from the RO plant to be used in the laboratory. This eliminated the need to produce 60 kL/week of distilled water (3 ML/yr), and saved $600 in water supply costs. The pipework installation cost $500.
38
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
3.8
Wastewater This section outlines typical wastewater treatment systems used in Australian dairy processing plants. Further information on wastewater management, trade waste discharge costs, yield optimisation and product recovery is presented in Chapter, ‘Yield optimisation’.
3.8.1
Treatment of wastewater The degree of treatment necessary to treat wastewater from a dairy processing plant is determined by the end use and criteria set by regulatory authorities — that is, whether the wastewater is to be discharged to sewer, reused on or off the site, discharged to surface water or used for irrigation. Processes used to treat wastewater fall into three main categories: • physico-chemical (for primary treatment) • biological (for secondary treatment) • disinfection (some forms of tertiary treatment). This eco-efficiency manual does not attempt to examine wastewater treatment in detail, so it is discussed only briefly in this section.
Primary treatment Primary treatments commonly used by the dairy industry are screening, equalisation, neutralisation, and dissolved or induced air flotation (DAF or IAF) to remove fats and suspended solids. Other primary treatments that are being trialled at some factories use ‘hydrocyclones’ which also remove fat and can be used in combination with air flotation units.
Primary treatment systems such as induced air flotation (IAF) are commonly used in the dairy processing industry to remove fats and suspended solids.
WATER
39
Secondary treatment Secondary treatment may incorporate the removal of organic matter and in some cases nutrients such as nitrogen and phosphorus. It typically uses a series of anaerobic and aerobic biological treatment processes. Secondary treatment relies on micro-organisms consuming and converting organic material in the wastewater into either carbon dioxide or methane (biogas), or into more cell matter (sludge) which can be removed and usually dewatered, stabilised and removed offsite. Further information on biogas and sludge utilisation can be found in Chapter 4, ‘Energy’ and Chapter 6, ‘Solid waste reduction and value adding’.
Tertiary treatment Tertiary treatments use biological and/or physical and/or chemical separation processes to remove organic and inorganic substances that resist primary and secondary treatment; they produce very high-quality effluent. The most common form of tertiary treatment used by the dairy industry involves the use of membranes, as described in sections 3.7 and 5.8.
3.8.2
Selection of a wastewater treatment system Selection of a wastewater treatment system will depend on: • the location of the plant • capital and operating costs • available space • the characteristics of the wastewater, such as types and load of contaminants, volume of wastewater and the variation in the generation of the wastewater over time • proximity to nearby residents • effluent quality, as specified by either the local authority or the regulator • the end use (e.g. is the water to be reused or recycled onsite or given/sold to a third party?) For dairy processing plants that have the option to discharge waste to the sewer, primary treatment is usually the highest level of treatment required; but plants in regional locations usually treat wastewater by secondary and tertiary methods to a level suitable for irrigation. Soil salinity is an aspect that must also be considered in some cases. Salinity of dairy effluent is affected mainly by the use of sodium hydroxide in cleaning and effluent neutralisation, as well a by the loss of salt during the manufacture of cheese and butter. An eco-efficiency approach to selecting and operating a wastewater treatment system considers: • the resources consumed by the treatment system, such as electricity, chemicals and oxygen
40
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
• opportunities for the system to recover valuable materials contained in the waste stream • opportunities to reuse water after treatment • opportunities to recycle biosolids or effluent after treatment • the ease with which the system can be operated • the efficiency of the wastewater treatment system in meeting regulatory requirements • the complexity of the process and risk of system failure. Where financially viable, wastewater treatments should be selected that enable existing and future opportunities for water reuse, product and energy recovery, and effluent or biosolid recycling. Again, from an eco-efficiency perspective, the most important step is to minimise the volume of wastewater and prevent waste from entering the wastewater stream in the first place. This is discussed in more detail in Chapter 5. Zero discharge of wastewater: Bonlac Foods, Stanhope Bonlac Foods in Stanhope will begin reusing 100% of its wastewater for irrigation in a project focusing on the sustainable reuse of water. Previously the water was irrigated to land over summer and to surface waters during winter. The project will involve building new storage and treatment lagoons and preparing more than 250 hectares of land for irrigation. Recovery of wastewater for ash sluicing: Bonlac Foods, Spreyton Bonlac Foods in Spreyton uses considerable volumes of water to sluice ash from the coal-fired boilers. A system was installed to recover treated wastewater for this purpose. Treated water is visually clear after treatment by the DAF plant, but has a moderately high dissolved BOD content. The system includes strainers to protect the pump and valves, and has an automatic backup supply of process water. The cost of the system is $34 000, with anticipated savings of $15 000/yr in water and trade waste charges.
3.8.3
Reuse of treated wastewater for irrigation Some wastewater streams from dairy processing plants in regional areas are used for irrigation. The suitability of wastewater for irrigation can vary according to: • the concentration of dissolved salts in the water, measured as electrical conductivity (EC) • the concentrations of specific salts such as sodium, phosphate and nitrates • soil type (e.g. permeability and how well it drains) • crop type (e.g. salt tolerance of particular species) • the climate (e.g. amount of leaching due to rainfall ) • method of irrigation (e.g. whether from overhead sprinklers, because wastewater with high salt levels may cause leaf burn).
WATER
41
Table 3.7 gives a general idea of the suitability of wastewater for particular sets of circumstances. The uptake of salts by crops and pasture can reduce growth, discolour or scorch leaves, or cause foliage death, so it is essential that the salinity level of wastewater used for irrigation is routinely monitored. A risk assessment that includes a water, nutrient and salt model should be developed to fully assess the hydraulic and nutrient salt loadings of the soil, and the likely impact of irrigation. It is also important to prevent runoff and contamination of waterways, and spray drift onto neighbouring lands. As a starting point, refer to the ANZECC Guidelines for fresh and marine water quality for information on quality of water that can be used for irrigation (ANZECC 1992). Table 3.7
Suitability of saline wastewater for irrigation Concentration of dissolved salts (EC units)
Conditions suitable for use of saline wastewater
1500–2500
For continued use, moderate to high leaching and salt tolerance needed.
2501–5000
Salt-tolerant crops; considerable leaching; and permeable, well-drained soils required for continued use.
5000
Should be used only on salt-tolerant crops, and usually only to supplement rain or low-salinity water.
Source: Goulburn-Murray Water 2001
42
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
4
Energy
4.1
Overview of energy use The dairy manufacturing industry has radically improved its energy efficiency over the last 20 years (in some cases by as much as 50%) through industry-wide upgrading of equipment and the closure of smaller, less efficient factories (Lunde et al. 2003). Dairy factories still use significant amounts of energy, depending on the types of products manufactured. Dairy factories producing mainly market milk use energy for heating and pasteurisation, cooling and refrigeration, lighting, airconditioning, pumping, and operating processing and auxiliary equipment. Factories producing concentrated milk products, cheese, whey or powders require additional energy for churning, pressing, separation, concentration, evaporation and drying. The sources of energy in Australian dairy processing plants are generally electricity and thermal energy from fossil fuels including coal, oil, natural gas and LPG, while a small number of plants supplement fuel supplies with biogas. In this section, energy use has been analysed for three categories of dairy processing plants: those where the primary product is white or flavoured milk, those that primarily produce cheese and whey, and those that produce mainly powdered products.1 Table 4.1 shows typical percentages of energy supplied from electricity and other fuels used to produce thermal energy (i.e. steam for Australian dairy plants surveyed during this project).
Table 4.1
Proportions of electricity and thermal energy use Electricity (%)
Thermal (%)
Milk only
66
34
Cheese and whey products*
27
73
Mainly powders
21
79
* excluding powders
Table 4.2 shows total use of energy (electrical and thermal) per kL of raw milk intake. As the table shows, these figures vary by around 18% for liquid milk plants and over 500% for plants producing mainly powders. The wide variation for powdered plants is mainly due to the differences in evaporating technology used. The median of these figures is around 45–65% of typical energy consumption in dairies in the UK. The Australian data also compares favourably with figures quoted by the International Dairy Federation. Electricity consumption for a range of plants was 0.22–0.47 GJ/t milk treated, and thermal energy consumption was 2.88–5.40 GJ (Kjaergaard-Jensen 1999); these are significantly higher than the Australian figures. In Canada, average electricity use was 0.61 GJ/kL for a liquid milk plant and 0.36 GJ/kL for a cheese, whey, powder plant, while for thermal use the figures were 1.06 GJ/kL and 1.07–1.38 GJ/kL respectively (Wardrop Engineering 1997); these are closer to the Australian data.
ENERGY
1
Energy data is based on a survey of Australian dairy processors. Figures are for a total of 17 plants including
1
5 primarily milk producers, 3 cheese and whey and 9 mainly powder producers.
43
Table 4.2
Total energy use — electrical and thermal UK data1
Australian data, this project
1
GJ/kL raw milk intake
Min.
Max.
Median
Variance %
No. plants providing data
Average
Milk only
0.46
0.54
0.47
17%
5
0.82
Cheese and whey products
0.39
0.75
0.63
92%
3
1.44
Mainly powders
0.48
3.03
1.32
531%
9
2.18
ETSU 1998
Figures 4.1 and 4.2 show the typical breakdown of energy costs in two UK dairy processing plants, one producing mainly white milk and the other producing cheese and powders. For a short shelf-life milk plant, energy costs are relatively evenly distributed between refrigeration, general services, processing, clean-in-place, bottling and cartoning. For plants producing cheese, whey and powders, the main energy costs are in drying and evaporating, followed by general services, refrigeration and clean-in-place. Figure 4.1
Energy cost breakdown by
Figure 4.2
area — milk plant Bottling and cartoning 12% Space heating 4%
Energy cost breakdown by area — powder, cheese and whey plant
General Services 19%
Air compressors 9% Milk processing 13%
Refrigeration and cold stores 18% CIP and washdown 13%
Bottle washing 12%
Effluent plant 5% Cheese/butter production 6% Separators 3% Air compressors 3%
Water pumps 2% General services 18%
Refrigeration and cold stores 10%
Evaporators 22%
Spray dryers 22%
CIP and washdown 9%
Source: ETSU 1998
There is scope for Australian dairy processors to reduce energy usage by implementing eco-efficiency initiatives, such as: • optimising the operations of energy-consuming equipment • recovering heat energy • optimising the plant’s load requirements with electricity supply demands • exploring alternative sources of energy • cogeneration.
44
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
4.1.1
The cost of energy Table 4.3 shows typical costs for the energy sources commonly used in dairy factories, which vary between approximately $2 per GJ for black coal and around $14 per GJ for electricity. It should be noted that there can be some variation in the price paid for fuels and electricity within the industry, depending on the supplier and the negotiating power of the business. Most dairy processing plants consume over 200 MW h/yr, making them eligible to choose their electricity supplier and purchase electricity on the contestable market where this is available.
Table 4.3
Typical costs for primary energy sources Fuel costs
Calorific value
Typical fuel cost ($/quantity of fuel)
($/GJ)
CO2 emissions kg CO2 equivalent/GJa
Black coal
27.84
MJ/kg
$55
/t
$1.98
92.7–98.1
Fuel oil
43.1
MJ/kg
$425
/t
$9.86
81.5
Natural gas
39.5
MJ/m3
$0.22b
/m3
$5.5b
61.8–70.8
3.6
MJ/kW h
$0.05
/kW h
$13.89
281–401
Electricity a
AGO 2004;
b
Typical cost in Victoria (NB: Typical cost of natural gas in Queensland = $12/GJ)
Table 4.4 shows typical fuel costs for steam production in coal, natural gas and oil-fired boilers. These costs do not include the operating costs of chemicals, labour, maintenance and ash disposal. The fuel costs for producing steam from coal is considerably lower than for gas and for fuel oil. As shown, the cost per tonne of steam is around $6.50 for a coal-fired boiler (85% efficiency) to over $16 per tonne for a natural gas boiler (95% efficiency). (Note: this does not include costs of labour or ash handling.) Table 4.4
Typical fuel costs for steam productiona Coal boiler (85% efficiency)
ENERGY
Fuel oil boiler (90% efficiency)
Energy content of steam
2.8
GJ/t steam
2.8
GJ/t steam
2.8
GJ/t steam
Fuel energy input
3.3
GJ/t steam
2.9
GJ/t steam
3.1
GJ/t steam
Quantity of fuel
118
kg coal/ t steam
74
m3 gas/t steam
72
kg oil/t steam
$6.47
/t steam
$16.28
/t steam
$30.50
/t steam
Cost a
Natural gas boiler (95% efficiency)
Based on a system producing steam at 11 bar and 184°C, with a steam enthalpy of 2.8 GJ/kg steam
45
Hot water is also used for heating and sterilisation. Table 4.5 shows typical fuel costs for water heating. Table 4.5
Typical fuel costs for direct heating of water with electricity or gas from 20°C to 84°C a Direct water heating
a
Electricity
Gas
95% efficiency
95% efficiency
Heat input required (MJ)
282
MJ/kL
282
MJ/kL
Quantity of fuel/power
78.2
kW h/kL
7.1
m3 gas/kL
Cost
$3.91
/kL
$1.69
/kL
Based on electricity price of $0.05/kW h and gas price of $0.22/m3
Replacement of electric heaters with steam heaters, Murray Goulburn Cooperative, Koroit Electric dryer bar heaters were replaced with heaters fuelled by steam. Savings in fuel have been estimated at $156 000/yr (including 1938 tonnes CO2 emissions) for an installation cost of $80 000.
4.2
Energy management A good energy management program will identify uses of energy for a factory and highlight areas for improvement. One of the first steps in an energy management program is to find out where energy is being used across the site, which may require the installation of additional instrumentation such as steam, gas and electricity submeters. Measuring and monitoring energy use will highlight opportunities for savings and in turn reduce greenhouse gas emissions. The formation of an energy management team, involving a wide cross-section of staff, is a proven way of identifying opportunities to reduce energy consumption. Energy management: Peters and Brownes, Balcatta Peters and Brownes at Balcatta has improved its energy management by creating a database of weekly operating information. Electricity is analysed by site area and charges are now split into areas. Gas is also metered to allow usage across the site to be analysed. Energy saving projects: Murray Goulburn, Maffra Murray Goulburn in Maffra has implemented a number of energy-saving initiatives, which have reduced total energy costs by 12%. Initiatives include:
46
•
forming an energy management team to identify energy issues
•
installing energy-efficient lighting
•
improving the operation of the refrigeration system compressors
•
more closely linking boiler operation to process plant requirements by improving communication between the boiler house and process operators
•
benchmarking plant start-up and shutdown times
•
tagging and measuring energy consumption of all relevant equipment items
•
repairing steam and air leaks and maintaining pipes.
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
Product scheduling improvements save energy: National Foods, Penrith National Foods in Penrith, by improving product scheduling and increasing throughput of the factory, has also saved in energy and water for washing the pasteuriser. Operating procedures dictate that the pasteuriser is cleaned every 9–14 hours, depending on the type of product. The product scheduling improvements have reduced the time for which the pasteuriser switches to recirculation mode (effectively not producing product), thereby reducing energy and water consumption per unit of product.
Demand management There are substantial savings possible through managing the electricity demand of the plant. Demand charges are based on the largest amount of electricity consumed in any single demand period (e.g. 15 minutes) during the billing period. Demand charges can therefore be decreased by managing the operation of equipment to utilise off-peak supplies, load shedding, and staggering the start-up times of large equipment items such as compressors or dryers. Soft starters on motors will also flatten out power demand during start-up. Reducing power demand: Murray Goulburn Cooperative, Leongatha Murray Goulburn in Leongatha conducted an electrical energy audit. The survey provided a better understanding of electrical load characteristics, an opportunity to better manage peak loads, and a basis for future selection characteristics for electrical equipment. The audit provided the framework for better managing variable production inputs. Potential savings in demand charges were estimated at $100 000. Challenges include having people underst and the ramifications of their actions when plant is started, and potential costs. Improved start-up procedures: Murray Goulburn Cooperative, Koroit A procedure was developed for plant start-up after power flicks at Murray Goulburn’s Koroit plant; this resulted in savings due to reduced peak loadings. Large equipment items are now started in sequence, which has reduced the maximum demand of the site.
4.3
Reducing the demand for steam and hot water
4.3.1
Evaporation Evaporators are commonly used in dairy processing plants to concentrate heat-treated milk from approximately 10% to around 50% total solids. Figure 4.3 shows a schematic of a falling film evaporator typically used by the industry. Evaporators may be single- or multiple-stage (effect) where energy savings are made by using the vapour from the first effect to heat product in the second, and so on. Energy consumption is reduced by increasing the number of effects, up to as many as seven for large factories in Europe (ETSU 1998). Thermal vapour recompressors (TVRs) further reduce energy usage by using a steam ejector to compress the vapour, increasing its temperature and pressure before utilising its evaporative energy. Mechanical vapour recompressors (MVRs), which use a motor or mechanically driven compressor, are even more energy-efficient than TVRs, even though additional electrical energy is required to operate the compressor. The most energy-efficient evaporators use a combination of multi-stage design and mechanical vapour recompression. Table 4.6 shows a comparison of energy
ENERGY
47
requirements for four combinations of evaporators. A study of five Australian milk powder factories indicated that a combination of TVRs, MVRs, multiple-stage evaporators (up to five) and multiple-stage dryers are currently used by the industry (Lunde et al. 2003).
Figure 4.3
Single-effect falling film evaporator schematic
Source: Tetra Pak Handbook, 1995
Table 4.6
Energy consumption of multi-effect evaporators and vapour recompression Technology
Typical specific energy consumption
Triple-effect evaporation
0.14 kW h per kg water evaporateda
Five-effect evaporation
0.085 kW h per kg water evaporateda
TVR + triple-effect evaporation
0.12–0.15 kW h per kg water evaporatedb
MVR + triple-effect evaporation
0.01–0.02 kW h per kg water evaporatedb
a
Joyce 1993
b
ETSU 1998
Use of mechanical vapour recompression: dairy processor, Japan Meiji Milk Products in Japan replaced a thermal vapour recompression evaporator (TVR) with a mechanical vapour recompression (MVR) system, and reduced evaporator operating costs by 75%. The MVR was installed on a four-effect evaporator with an evaporation rate of 30 t/h. The TVR had operating costs of US$680 000/yr, while the MVR required only US$175 000/yr. The cost of the new MVR was US$1.5 million compared to US$1.3 million for a new TVR evaporator. Source: CADDET 1992
48
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
4.3.2
Membrane concentration Membranes are often used to concentrate dairy streams in preparation for further processing. For example, ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) membranes have been used to concentrate whole milk, skim milk, whey and protein streams (Koch 2004; PCI-memtech 2000). Membrane processes are energy-efficient for concentration, with typical energy consumption around 0.004–0.01 kW h per kg of water removed (ETSU 1998), which is significantly more economical than using evaporation methods (Table 4.6). However, there are economic limitations to the level of concentration that can be attained, to the point where it is financially preferable to use traditional evaporation methods. For example, whey is concentrated up to 18–27% because beyond that range process performance is reduced, due to the high osmotic pressure, high retentate viscosity, lactose crystallisation and calcium phosphate precipitation (Daufin et al. 2001). The more concentrated the retentate, the higher is the pressure and the more robust the membranes required for filtration. Membranes have been used to concentrate streams to up 55% total solids (PCI-memtech 2000), primarily determined by viscosity and fouling considerations. Pumping equipment will also be more energy-intensive, which will lead to higher operating costs. Further information on membranes can be found in ‘Cost-effective membrane technologies for minimising wastes and effluents’ (WS Atkins Consultants Ltd 1997). Thickening and desalinating whey in the dairy industry: dairy processor, The Netherlands1 Before food ingredients can be made out of whey, the original thin liquid must be concentrated and desalinated. A whey processing plant in The Netherlands has installed a nanofiltration unit to perform part of the total thickening process. The membrane filter replaces an evaporator and ion exchanger; this increases the solids content of the whey from 5.5% to 17%, and removes 70% of the salt content with the permeate. Steam consumption for the old system was 436 m3 natural gas equivalent (NGE) per tonne dry solids, and electricity consumption was 11.5 m3 NGE/t. Steam use for the new system has decreased to 120 m3 NGE/t but electricity consumption has increased to 19.2 m3 NGE/t. Net energy savings are 308 m3 NGE/t, which equates to around 70% of the original energy consumption. In addition there were savings in chemical and water use for cleaning. The payback period was 1.3 years.1 1
4.3.3
CADDET 1999
Spray drying Spray drying is used extensively by the dairy industry for producing powdered milk, whey and cheese. It involves atomising the feed into a spray of droplets which are put into contact with hot air in a drying chamber. Spray dryers are usually used in conjunction with evaporators, and dry product from around 50% solids through to 97% solids. The energy consumed in spray drying is reported at around 0.05–0.1 kW h per kg of water removed (ETSU 1998). Dryers may be co-current, counter-current and mixed flow, with sprays produced by a rotary (wheel) atomiser or nozzle atomiser (Schuck 2002). Spray dryers may be single, two-stage or multi-stage, with the latter being the most energy-efficient but also the most capital-intensive. Second and later stages use fluidised bed drying, which is more energy-efficient.
ENERGY
49
A useful measure of the dryer efficiency is specific energy consumption (SEC), which measures how much energy is required per kilogram of water evaporated from the feed, where: SEC (kJ/kg) = rate of energy consumption of dryer (kW) / rate of evaporation of dryer kg/s The evaporative rate, E, in kg vapour/s is given by: E = WS (X1 – X0) where WS = dry solids feed rate and X1 and X0 are the moisture contents of the input and output streams defined as a fraction of the dry solids weight. The rate of energy consumption should be routinely monitored and compared against other similar spray dryers. Tips for the efficient operation of a spray dryer include: • operating the plant at full design rating • maximising the solids content of the milk concentrate, to achieve good atomisation at the spray nozzle or atomiser • minimising the loss of waste heat from the exhaust (It is desirable to use high inlet air temperatures and low exhaust air temperatures, to achieve the required degree of drying. This can be achieved through two-stage drying, where a fluid bed dryer is installed to reduce residual moisture content of the product to an acceptable level, hence allowing the dryer to run with lower exhaust air temperatures.) • recovering waste heat by installing a recuperator that uses exhaust air to pre-heat the inlet air • investigating ways of pre-heating the milk concentrate. There can be problems with recuperating waste heat, due to the presence of particulates in the exhaust air stream and the tendency for fouling, which causes hygiene problems. This technology is no longer in use in Australian dairy factories for this reason. A more detailed discussion on heat recovery systems and the efficient operation of spray dryers can be found in Good Practice Guide 185 of the UK Energy Efficiency Best Practice Programme, Spray drying (ETSU 1996). The energy efficiency of the dryer can be maximised by maximising the solids content of the feed — for example, operating at 40% solids instead of 30% reduces the heat input by 36% (ETSU 1996). As a rule of thumb, every 0.5% increase in feedstock solids reduces energy consumption by 2%. ETSU 1996
50
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
Improved start-up procedures for evaporator and dryer: Murray Goulburn Cooperative, Rochester1 The Murray Goulburn Energy Management Team (EMT) in Rochester identified energy saving opportunities for the Niro evaporation and drying plants at their Rochester (Victoria) branch. By monitoring the amount of steam used during plant start-up, the EMT saw opportunities to reduce steam usage. It was found that too much time was spent heating the evaporator and dryer on start-up. Reducing the heating time reduced the amount of steam used. The EMT estimated potential annual savings of $23 000 from reduced steam usage. Heat recovery from spray dryer: Tatura Milk, Tatura2 Tatura Milk Industries’ recently installed milk powder plant has included heat recovery on the gas-fired heater. The spray dryer uses 4.5 t/h of steam, 22 GJ/h of gas and 550 kW h of electricity, to produce 5.5 t/h of whole milk powder.
4.3.4
1
ITR 2003
2
Niro 2003
Boiler operation There are some basic items that should be considered for the efficient operation of boilers; these are discussed briefly below. For expert advice on the operation and maintenance of your boiler, it is best to contact your supplier, maintenance contractor or in-house engineer.
Check the fuel-to-air ratio and compare readings with optimum gas percentages The efficiency of a boiler can be monitored by measuring the excess air and the composition of flue gas. Insufficient excess air will lead to incomplete fuel combustion, while too much causes a loss of heat in the boiler and a decrease in efficiency. Optimum percentages of oxygen (O2), carbon dioxide (CO2) and excess air in exhaust gases are shown in Table 4.7. The ratio of boiler air to fuel can be adjusted to obtain the optimum mix of flue gases, using oxygen trim systems. Table 4.8 shows the potential fuel savings resulting from the installation of online oxygen trim control. Such systems usually reduce energy consumption by 1.5–2%, with a typical payback period ranging from a few months to 2 years (SEAV 2002a). Table 4.7
Optimum flue gas composition Fuel
O2 (%)
CO2 (%)
Excess air (%)
Natural gas
2.2
10.5
10
Coal
4.5
14.5
25
Liquid petroleum fuel
4.0
12.5
20
Source: Muller et al. 2001
ENERGY
51
Table 4.8
Fuel savings from installing online oxygen trim control Boiler capacity (MW)
Fuel savings (GJ/yr)
Fuel savings ($/yr)
CO2 (t/yr)
Simple payback (yr)
0.5
318
3 816
19
2.0
1
635
7 620
37
1.0
2
1270
15 240
75
0.5
4
2540
30 480
150
0.2
6
3810
45 720
224
0.2
8
5080
60 960
299
0.1
10
6350
76 200
374
0.1
Source: Adapted from SEAV 2002a Assumptions: gas costs $12/GJ; boilers operate 24 h/day, 350 days/year; installation cost of the boiler trim system $7500
Oxygen trim controller on boilers: Peters and Brownes Foods, Roxburgh Peters and Brownes Foods in Roxburgh is investigating the installation of an oxygen trim controller on its boiler, which is expected to reduce gas usage by 2% and save $10 000/yr for a cost of $30 000.
Regularly record the flue gas temperature A good benchmark for the operation of the boiler can be established by measuring the stack gas temperature immediately after the boiler is serviced and cleaned. The stack gas temperature can then be regularly monitored and compared with the optimum reading at the same firing rate. It is estimated that there is a 1% efficiency loss with every 5oC increase in stack temperature (Muller et al. 2001). A major variation in stack gas temperature indicates that there has been a drop in efficiency and the air-to-fuel ratio needs to be adjusted, or the boiler tubes cleaned.
Operate the boiler at the design working pressure It is important to ensure boilers are operating at their maximum possible design working pressures. Operating them at lower pressures will result in lower-quality steam and reduced overall efficiencies. If the system requires lower pressures, use pressure-reducing valves. The general rule is: generate and distribute steam at high pressure and reduce it to the lowest possible pressure at the point of use (Manfred Schneider 2004, pers. comm.).
Monitor and clean boiler tubes to remove scaling Scale acts as an insulator and inhibits heat transfer. A coating of scale 1 mm thick can result in a 5% increase in fuel consumption, and if the thickness is allowed to increase to 3 mm the fuel consumption can increase by 15% (MLA 1997). So preventing the build-up of scale by treating the boiler feedwater can result in significant energy savings. Not only does scale increase fuel consumption but, if left untreated, it will also reduce the life expectancy of the boiler.
52
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
The treatment of boiler feedwater will help to minimise build-up of scale, which acts as an insulator and inhibits heat transfer.
Match steam supply with demand If the steam production at the boiler house is too high compared to the plant’s actual steam demand, the excess may need to be vented, resulting in unnecessary fuel wastage. The use of metering instrumentation (steam, water and fuel meters) will help match steam supply with demand. If appropriate, meter the steam flow to different sections of the plant separately. Improving communication between boiler operators and end users can lead to significant savings in boiler operating costs. It is not uncommon for boilers to be operated inefficiently at low load or on standby ready to meet process demands. Improving communications can allow the boilers to be operated more efficiently at higher loads for the periods required, thereby reducing operating costs. Boilers should be started up as late and shut down as early as possible while still meeting process demands. This is more difficult to manage with solid fuel boilers than with gas or oil, due to the slower response time. Variable demand during the day, especially when it peaks for short periods (for example when large capacity plant is first started), can be accommodated by using a ‘steam accumulator’ — a large vessel filled with water that is heated by the steam to steam temperature. Steam that is not needed to heat the water simply flows through it and out to the plant; but when a sudden peak load is imposed a proportion of the water in the tank is ‘flashed off’ into steam at the reduced pressure, thus protecting the boiler from instantaneous loads. This kind of system can effectively meet short-term demands that are considerably in excess of the boiler’s rated output (Manfred Schneider 2004, pers. comm.). Improving steam-raising efficiency: Murray Goulburn Cooperative, Rochester1 Murray Goulburn at Rochester formed an Energy Management Team (EMT) which identified inefficiencies in boiler operation due to communication problems between boiler and process operators. The boilers were operated at low load (and lower efficiency) so they could quickly increase steam supply at any time to meet production demands. The EMT developed new procedures and a communications plan for the site to improve communication. The average load of one boiler was increased from 30% to 60%, contributing to a 4% increase in steamraising efficiency. The savings on the one boiler are estimated at $180 000/yr, with greenhouse gas emission reductions of 1536 t. 1
ENERGY
ITR 2003
53
4.3.5
Steam delivery Rectification of steam leaks Leaks allow live steam to be wasted, causing more steam production to be required to meet the plant’s needs. As more replacement feedwater is required, more fuel is used for heating and more chemicals are needed for treatment. For example, a hole 1 mm in diameter in a steam line at 700 kPa will lead to a annual loss of 3000 L of fuel oil or 4300 m3 of natural gas, equating to around $2000 (SEAV 2002b). Elimination of steam leaks: Bonlac Foods, Spreyton Bonlac Foods in Spreyton generates steam and distributes it at 4000 kPa — the pressure required for spray dryer air heating. All other duties use steam at 1000 kPa which is produced at four ‘letdown’ stations located near the points of use. Design faults at the letdown stations allowed continual leakage of steam. The stations were rebuilt with heavy-duty automated isolating valves and improved design. The improvements saved $71 300 in coal supply costs. The cost of implementation was $147 000. The completion of the project was delayed by the difficulty in scheduling windows in the production schedule to allow installation; but the project could have been avoided if the design of the steam equipment had been examined more critically during construction.
Boiler condensate return systems Boiler condensate (as opposed to evaporator condensate) contains valuable heat energy. It should be returned to the boiler feed tank to save water and utilise this energy, unless it is excessively contaminated with product or corrosive elements. If it is contaminated, the heat it contains could be recovered (e.g. via a heat exchanger to the cold make-up water). If contamination is only a possibility, various contamination detection systems are available (usually conductivity meters) to enable its normal recovery or rejection to waste if contaminated. A 5°C increase in the temperature of the feedwater will save around 1% of the fuel used to raise steam (SEAV 2002a). In addition, the water has usually been chemically treated already, thus saving treatment costs. Condensate return systems are often designed with flash vessels to allow for the re-evaporation of condensate into steam (referred to as flashing). The flash vessels also remove non-condensable gases such as air and CO2. If these gases remain in the equipment being heated, the gases form pockets that insulate the heat transfer surface and decrease boiler efficiency (Graham Smith 2004, pers. comm.). The steam in the flash vessels can be used as a low-grade heat source.
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ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
Condensate return: National Foods Ltd, Murray Bridge At National Foods in Murray Bridge a system was installed to recapture condensate from the large steam users and return it to the boiler. This has reduced the running costs of the boiler and reduced the use of boiler chemicals. Challenges included installing the pumps and pipework for the return line to the boilers on an existing system. Condensate return lines should be installed with the boiler, saving time and effort upfront. Improved condensate return: Murray Goulburn, Rochester1 Murray Goulburn in Rochester, as part of the Energy Efficiency Best Practice project of the Australian Government Department of Industry, Tourism and Resources (ITR), identified savings of around $200 000/yr in natural gas costs by improving the efficiency of the condensate return system, repairing steam leaks and improving maintenance of pipes. By insulating condensate return pipes, boiler feedwater temperature could be increased from 45°C to 65°C, thereby increasing the boiler efficiency by 3.3%. 1
ITR 2003
Maintenance of steam traps A steam trap is an automatic valve for removal of condensate from a steam system. In the presence of steam it closes, preventing steam from being passed through it and being wasted before it has given up its heat and condensed. In the presence of water it opens, allowing the discharge of condensate. Depending on its type, it may also open to discharge non-condensable gases. Where feasible, condensate removed from steam traps should be returned to the boiler feed tank as previously discussed. Regular testing and maintenance of steam traps and condensate lines saves money and time as well as improving operating efficiency. Traps can be checked by plant staff or an outside contractor. Traps that are losing steam can waste thousands of dollars a year, usually far more than the cost of their replacement or repair (Smith 2004, pers. comm.). Steam system audit: Murray Goulburn Cooperative, Leongatha Murray Goulburn in Leongatha undertook a steam system audit to review the efficiency of the many steam traps. It cost the plant $10 000 to eliminate the faulty/leaking traps. Savings have not been quantified.
‘Be proactive. The savings are the result of fixing a large number of small out-of-the-way items.’ — Ted Isaacs, Murray Goulburn Cooperative, Leongatha
Rationalisation of boiler use and steam lines For some older factories that have progressively expanded over the years, steam supply lines may not take the most direct route from the boiler to the point of use. This results in a greater length of steam pipework than is really required and greater opportunity for heat loss and leaks. Rationalising steam and condensate pipework can lead to savings in boiler operating costs. A review of boiler use may also identify the need for a boiler upgrade or even replacement.
ENERGY
55
Rationalised steam supply: Peters and Brownes Foods, Roxburgh Peters and Brownes Foods in Roxburgh reduced gas usage by $10 000/yr and maintenance costs by $15 000 by decommissioning two boilers for the ice-cream plant and using steam from existing beverage plant boilers. The cost of implementation was $65 000, with a payback period of less than 1.5 years.
Insulation of pipes Uninsulated steam and condensate return lines are a source of wasted heat energy. Insulation can help reduce heat loss by as much as 90%, as shown in Table 4.9. Insulation that is damaged should be repaired and sources of moisture should be removed to prevent insulation from deteriorating. It is estimated that 35% of the heat energy supply is lost during the manufacture and distribution of steam, while approximately 2000 kW h is lost in a year from a 1-metre length of 5cm steam pipe with a surface temperature of 170°C (Kjaergaard-Jensen 1999). Table 4.9
Heat loss from steam lines Level of insulation
Heat loss (MJ/m/h)
Steam loss (kg steam/m/h)
Equivalent fuel cost (gas) per 50 m pipe per year
Uninsulated
2.83
1.0
$3396
Insulated with mineral fibre
0.138
0.05
$165
Source: Adapted from US DOE 2002 Assumptions: 125 mm steel pipe at 150°C; natural gas cost of $0.012/MJ of boiler operating 8 h/day, 250 days/year.
Insulation of pipes: Murray Goulburn Cooperative, Leitchville Murray Goulburn in Leitchville made repairs to the insulation of various steam and condensate pipes. The expenditure was $12 000, with a 6-month payback period. Insulation of steam lines: Dairy Farmers, Jervois Dairy Farmers in Jervois are planning to upgrade insulation on their steam lines. It is estimated that 30 kW of energy is radiated per metre of pipe, and pipes are approximately 60 m long.
4.3.6
High-efficiency boilers Boiler efficiency can be improved by installing heat recovery equipment such as economisers or recuperators. An economiser is an air-to-liquid heat exchanger that recovers heat from flue gases to pre-heat boiler feedwater. Fuel consumption can be reduced by approximately 1% for each 4.5°C reduction in flue gas temperature (Muller et al. 2001). Recuperators are air-to-air heat exchangers that are used to recover heat from flue gases to pre-heat combustion air.
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ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
Combustion air blower variable speed drives can be retrofitted to continually match the load on the boiler. When replacing or upgrading boilers, many dairy processing companies are also investigating the option of converting to a more efficient and cleaner fuel (e.g. coal or fuel oil to gas). The installation of these energy-saving measures can mean an improvement in boiler efficiency from around 90–94% for a new boiler. The environmental impacts of switching fuels will be reduced (less greenhouse gas emissions), but the disadvantage is the higher cost of natural gas as shown previously in Table 4.4. Energy-efficiency in boiler design: Bonlac Foods, Darnum Park1 Bonlac Foods in Darnum Park increased the efficiency of their four 10 MW boilers by installing economisers, oxygen trim control, variable-speed drives and automatic blowdown control. Around 80% of the condensate is returned to the boilers, utilising heat in the condensate and reducing water consumption, chemical consumption and wastewater generation. 1
AGO 2002a
4.4
Reducing the demand for electricity
4.4.1
Refrigeration systems The energy cost of a refrigeration system can approach 20% of the total energy costs in a liquid milk processing plant (Figure 4.1). Dairy processors typically use the vapour compression cycle refrigeration system consisting of a compressor, condenser, evaporator and expansion valve. The most common refrigerant is ammonia. The efficiency of a refrigeration system is measured by the coefficient of system performance (COSP) which is the quantity of refrigeration produced (cooling output in kilowatts) divided by the total energy required by the system (energy input in kilowatts). The higher the COSP, the higher is the efficiency of the system. A useful software model, Coldsoft, is available from the Australian Dairy Processing Engineering Centre (DPEC 2003b). The model allows plant personnel to review and improve the performance of dairy site refrigeration systems.
Compressors The purpose of the compressor is to draw low-pressure refrigerant vapour from the evaporator, and compress it so the vapour can be condensed back into a liquid by cooling with air or water. The compressor is the workhorse of a refrigeration system and usually accounts for between 80% and 100% of the system’s total energy consumption (Carruthers 2004, pers. comm.). It is important, therefore, that the system operates under optimum conditions. The amount of energy used by a compressor is affected by the: • type of compressor • compressor load • temperature difference of the system (i.e. the number of degrees by which the system is required to cool).
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57
Compressor selection There are three main types of compressor used for refrigeration — reciprocating, rotary screw and scroll. Centrifugal compressors are often used for air-conditioning systems. It is important when selecting a compressor to choose a type best suited to the refrigeration duty and one that will enable the system’s COSP to be as high as possible.
The compressor is the workhorse of a refrigeration system and usually accounts for between 80% and 100% of the system’s total energy consumption.
Compressor load The compressor’s capacity needs to be matched with the load. If a compressor is not required, or is oversized, it operates at only partial load and the energy efficiency may be reduced. The use of multiple compressors with a sequencing or capacity control system to match the load can help to improve efficiency. In some cases, even with a capacity control system an oversized compressor will still be inefficient as a result of frequent stopping and starting. Some compressors are more efficient than others at part load, depending on the method of capacity control, and it is best to ask the manufacturer for a profile of efficiencies at varying load conditions. Ice banks can be an effective way of meeting peak demands without the need for large compressor capacity. They are best used in applications where there are short to medium peak loads but a much lower average load during a production day. Ice can be formed during the night to take advantage of cheaper off-peak electricity.
58
ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
Installation of new condenser: Dairy Farmers, Booval Dairy Farmers in Booval installed a new condenser to reduce the operating head pressure and save on the operating costs of the refrigeration plant. The payback on capital investment was 2 years. Challenges included the selection of a condenser to comply with noise limits.
Minimising temperature difference Compressors are most efficient when the condensing temperature (and therefore pressure) is as low as possible and the evaporating temperature (pressure) is as high as possible, while still meeting the refrigeration duties. Increasing the evaporating temperature will increase the compressor efficiency, so the thermostats should not be set lower than necessary. For example, it is cheaper and requires less energy to cool a stream down to 4°C than to 2°C. Less heat energy will be absorbed into the refrigerant, which in turn will reduce load on the compressor. In some cases this may not be possible, due to production temperature and humidity requirements; but do not cool more than is required. Alternatively, the condensing temperature can be decreased by ensuring that the condenser, which may be a water- or air-cooled cooling tower, is operating efficiently. Condensers should be sized correctly to maintain the optimum condensing temperature within the capabilities of the refrigeration system. If the condenser is too large, however, the refrigerant can actually sub-cool2 and this will affect the function of the expansion valve. A refrigeration system with a small evaporator and condenser may require a smaller initial capital outlay; however, running costs may be greatly increased by the need for a larger compressor, so this should be avoided. An increase of 1°C in evaporating temperature or a reduction of 1°C in condensing temperature will increase the compressor efficiency by 2–4%. ETSU 2000
Energy management control system: Nestlé, Victoria1 A Nestlé ice-cream plant in Victoria uses electricity worth around $960 000/yr. About 13 GW h of this electricity is used by the refrigeration system. A feasibility study for the refrigeration system showed that the compressors were operating under no load, there were numerous compressor start-ups, and the suction temperature of 12°C into the compressors was far above design temperature of 3°C due to incorrect valve selection. The minimum condenser pressure was also being maintained at around 1000 kPa over the winter months. The study recommended upgrading the current control system to improved valve selection so that the correct suction gas temperature (3°C) could be recovered, enabling the compressors to operate at higher loading and minimise stopping.
ENERGY
1
SEAV 2002b
2
Subcooling refers to cooling of the refrigerant below its saturation point (the point at which liquid turns into a vapour).
59
The study also suggested modifying the condenser pressure to operate at a minimum condenser pressure of 750 kPa instead of the existing 1000 kPa. The project cost the company $59 000 and installation took 4 months. Nestlé now saves $100 000/yr in electricity costs. Compressor start-ups were reduced by 92% and the run hours by 22%. There was an overall reduction in maintenance costs for the refrigeration plant of 20%.
The cost of operating a refrigeration system can be up to around 20% of total energy costs in a dairy processing plant.
Hot gas bypass defrost Hot gas from the outlet of the refrigeration compressor can be used to defrost freezers, but the control must be accurate. The defrost water may then be used elsewhere in the plant. Once installed and optimised, a hot gas bypass defrost system can ensure frost-free evaporator operation. Once the evaporator is no longer covered in ice its cooling capacity will be increased.
Reducing load on refrigeration systems Up to 10% of the power consumption in refrigeration plants can be from heat ingress through doorways in coolrooms. Many plants rely on good operator practice to keep doors closed, but this is not always effective. Automatically closing doors or an alarm system could be considered; and plastic strip curtains or swinging doors are useful at frequently opened entrances.
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ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
Lights and fans also add to the heat load. Sensors and timers can be used to ensure that lights are used only when necessary. Variable speed drives, coupled with a programmable controller, can cycle off fans and refrigerant feed during low load times. Cooling water loops using water at ambient temperature have also been used by some dairy processors to pre-cool high-temperature fluids (around 90°C) before chilling, thereby reducing the load on the refrigeration system.
Absorption refrigeration Absorption chillers allow cooling to be produced from heat sources such as clean fossil fuels, incinerated garbage, biofuels, low-grade steam, hot water, exhaust gas or even solar energy, usually using a lithium bromide and water refrigerant (Broad Air Conditioning 2004). The COP of absorption refrigeration, however, is relatively low compared with vapour compression refrigeration systems with the best absorption chillers generating just over 1 kW of refrigeration for 1 kW of energy. The higher the temperature of the waste heat, therefore, the more effective the refrigeration will be. The advantages of absorption chillers are that they can utilise a waste heat source with lower greenhouse gas emissions compared to conventional vapour compression refrigeration systems. Use of absorption refrigeration: milk processing plant, USA1 Honeywell Farms used a lithium bromide absorption chiller to cool liquid refrigerant of the main refrigeration system below its saturation temperature. The absorption chiller operated using waste heat from a compressor driven by a natural gas engine and increased the capacity of the existing refrigeration system by 8–10% by reducing the load on the compressor. Energy savings were calculated at US$90 400/yr, for an extra capital cost of US$339 549 compared with that of a standard plant and a payback period of 3.8 years. 1
4.4.2
CADDET 1996a
Compressed air systems Compressed air is used extensively in dairy processing plants, mainly for the operation of valves, filling and packing machines, and for cleaning spray dryer bag filters. The cost of operating a compressed air system in a dairy processing plant can approach 10% of total electricity costs (Figure 4.1). Compressed air systems are very energy-inefficient, with around 80% of electricity input lost as waste heat. A compressor will usually consume its purchase price in electricity every year (US DOE 2004b) and therefore selecting and efficiently operating the correct type of compressor for the application can substantially reduce operating costs, as discussed in the sections that follow. Installing a control sequencing system on multiple compressors will help the system to respond more efficiently to varying loads. Variable-speed compressors can reduce power with reduced demand. If compressors operate at variable rates or are oversized to cater for higher than usual loads, consider installing a variable speed drive (see section 4.4.4).
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61
Lead-lag system for compressors: Murray Goulburn Cooperative, Koroit The air compressors at Murray Goulburn’s Koroit plant were changed to a lead-lag system which reduced energy consumption by approximately 10%. One compressor is set as the lead compressor, which operates until it can no longer meet demand. The second or lag compressor is then automatically switched on. A lead-lag system prevents both compressors operating at once when not actually required. The cost of implementation was $5000, with annual savings of approximately $3000.
Compressed air leaks Leaks in a compressed air system can contribute 20–50% of total air compression output (SEAV 2002b). Table 4.10 indicates the cost of compressed air leaks. Ultrasonic detectors can be used to check for leaks; the traditional method of using soapy water on pipework is also effective. It is best to check for air leaks when the plant is shut down and background noise is minimal. It is also a good housekeeping measure to isolate compressed air on items of equipment that are shut down for extended periods (e.g. overnight or on weekends). Table 4.10
Cost of compressed-air leaks Equivalent hole diameter (sum of all leaks)
Quantity of air lost per single leak (m3/year)
Cost of single leak ($/year)
Less than 1 mm
12 724
$153
From 1 to 3 mm
64 415
$773
From 3 to 5 mm
235 267
$2823
Greater than 5 mm
623 476
$7482
Source: SEDA 2003 Assumptions: 700 kPa system operating for 4000 h/yr; electricity cost of 8 cents/kW h
Optimising air pressure Air pressure should be kept to the minimum required for the end use application. Sometimes operating pressures are set high to meet the demand of just one or two items of equipment. It may be possible to redesign individual items of equipment to enable pressure reduction across the plant. Alternatively, determine whether it is cost-effective to use a second compressor to service these equipment items. Table 4.11 illustrates the cost and energy savings that can be made by reducing air pressure. Compressed air is an expensive medium and its use should be avoided for activities such as cleaning or drying, where other methods such as fans or blowers could be used. It is estimated that every 50 kPa increase in pressure increases energy use by 4% (SEDA 2003).
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ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
Table 4.11
Cost and energy savings that can be made by reducing air pressure Air pressure reduction 50 kPa Average Energy load saving (kW) (kW h/yr)
100 kPa
Cost savings ($/yr)
Energy saving (kW h/yr)
150 kPa
Cost savings ($/yr)
Energy saving (kW h/yr)
200 kPa
Cost savings ($/yr)
Energy saving (kW h/yr)
Cost savings ($/yr)
4
320
26
640
52
960
78
1280
104
7.5
600
48
1200
96
1800
144
2400
192
11
875
70
1750
140
2625
210
3500
280
15
1195
96
2390
191
3583
287
4780
382
30
2390
191
4780
382
7170
574
9560
764
55
4380
350
8760
701
13 104
1048
17 520
1402
110
8760
701
17 520
1402
26 280
2102
35 040
2803
Source: SEAV 2002b Assumptions: 700 kPa system operating for 2000 h each year; electricity tariff 8 cents/kW h
Reducing inlet air temperature Up to 6% of a compressor’s power can be saved by using cooler air (SEAV 2002). When the inlet air entering a compressor is cold, less energy is required to compress it. The air should also be clean, as clogged filters at the inlet will cause a drop in pressure, reducing compressor efficiency. It is estimated that every 3°C drop in inlet air temperature decreases electricity consumption by 1% (SEDA 2003). Compressed air systems should be well ventilated and any hot compressor room air ducted away, perhaps to a heat recovery system for space heating. Table 4.12 shows energy and cost savings that can be made by reducing the temperature of compressor intake air. It is estimated that every 3°C drop in inlet air temperature decreases electricity consumption by 1%. SEDA 2003
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63
Table 4.12
Energy and cost savings from reducing the temperature of compressor inlet air Reduction to intake air temperature 3°C Average Energy load saving (kW) (kW h/yr) 4
6°C Cost savings ($/yr)
10°C
Energy saving (kW h/yr)
Cost savings ($/yr)
Energy saving (kW h/yr)
20°C
Cost savings ($/yr)
Energy saving (kW h/yr)
Cost savings ($/yr)
80
6
160
13
264
21
528
42
150
12
300
24
495
40
990
79
15
300
24
600
48
990
79
1 980
158
30
600
48
1200
96
1 980
158
3 960
317
55
1100
88
2200
176
3 625
290
7 251
580
110
2200
176
4400
352
7 260
581
14 520
1162
160
3200
256
6400
512
10 550
844
21 100
1688
7.5
Source: SEAV 2002b Assumptions: 700 kPa system operating for 2000 hours each year; electricity tariff 8 cents/kW h
Heat recovery from air compressors As previously mentioned, as much as 80% of the energy used to operate an air compressor is lost as heat. There are heat recovery units available that will recover heat from both water- and air-cooled compressors. However, heat recovery units for water-cooled compressors are more efficient and can provide a more significant payback on capital outlay. The energy recovery system consists of a plate heat exchanger, which transfers heat from the compressor’s lubricating oil to the water. This can heat water to up to 90°C and recover up to 70% of the compression heat without any adverse influence on the compressor performance. For example, a heat recovery unit for a 37 kW single-stage, oil-injected rotary screw compressor unit has the capacity to produce 36 L/min of 73°C hot water (Atlas Copco 2003).
4.4.3
Homogenisers The control of homogeniser pressures, in particular pressure drop, will affect the efficiency of the homogeniser and the quality of the product. Confusion in terminology for measuring pressure (e.g. gauge, absolute and differential pressure) can lead to homogeniser pressure settings that are less than optimum. Once an optimal pressure control strategy is established and understood, the energy consumption of the homogeniser can also be calculated and incorporated into plant energy-management programs. These aspects are explained further in the DPEC publication Homogeniser performance evaluation guide manual 1996/97 (DPEC 1996/97).
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ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
4.4.4
Motors Selecting a motor An electric motor uses 4–10 times its purchase price in electricity annually (AGO 2003b). When choosing a motor, it is therefore wise to consider the operating costs as well as the initial purchase price. High-efficiency motors cost up to 40% more than standard motors; however, energy savings quickly recover the extra cost, usually within two years. Table 4.13 illustrates the payback periods for motors with different ratings.
Table 4.13
Payback periods for purchasing high-efficiency motors Motor rating
High efficiency 11 kW
Standard
Standard
11 kW
High efficiency 45 kW
92
88.5
94.6
93.1
6000
6000
6000
6000
Average energy cost (cents/kW h)
10
10
10
10
Purchase price ($)
922
877
2390
1680
Annual operating cost ($)
7170
7450
28 541
29 032
Efficiency (%) Hours of operation per year
'
Payback on premium
2 months
45 kW
17 months
Source: Teco Australia 2003
Sizing a motor It is best to avoid purchasing oversized motors to cater for future production increases, either as insurance against motor failure or simply to override load fluctuations in the production processes. Motors that are oversized run with lower efficiency and power factor. If the load is constant, size the motor as closely as possible to the load, with a small safety margin. Table 4.14 illustrates savings to be made by replacing oversized motors with motors of the correct size to meet the load — for example in Case 1 the installation of a 3.7 kW motor which is 80% loaded, compared to 7.5 kW which is 40% loaded, saves $722/yr. Table 4.14
Cost comparison for oversized motors Case 1: Motor sizea
Case 2: Motor sizeb
7.5 kW (40% loaded)
3.7 kW (80% loaded)
110 kW (68% loaded)
75 kW (sized to match need)
Annual energy use (kW h)
17 813
8788
627 000
427 500
Annual energy cost (A$)
$1425
$703
$51 160
$34 200
Annual energy saving (A$)
$722
$16 960
Source: Adapted from US DOE 2004c a
Operating 2500 h/yr
b
Operating 6000 h/yr
Assumption: electricity cost $0.08/kW h
ENERGY
65
Information on best practice in motor management can be found on the Australian Greenhouse Office ‘Motor solutions online’ website, . The site includes a checklist, self-assessment tool, case studies and technical guides. Information on selecting the most suitable motor for different applications can be found on the US Office of Industrial Technologies Energy Efficiency and Renewable Energy website: Motor selector software, and the US Department of Energy website: Buying an energy efficient motor, .
Rewinding motors Although failed motors can be rewound, it is often better to take the opportunity to replace the motor with an energy-efficient model. It is suggested that an energy-efficient model should be purchased in preference to rewinding when the motor is less than 30 kW and the cost of rewinding exceeds 65% of the cost of a new motor (US DOE 2004a).
Variable speed drives Variable speed drives (VSDs) reduce energy consumption by adjusting the motor speed to continually match the load of equipment such as pumps, fans and compressors. VSDs are ideal for equipment that has to operate at variable loads or be oversized to cater for occasional high loads. The energy consumed by fans and pumps is proportional to the cube of the motor speed. For example, if a VSD on a refrigeration compressor reduced its speed by 20% the power consumed would drop by 49%. The installation of VSDs can be financially viable, but depends on the motor application and operating hours. VSDs are most economically viable for large motors. Table 4.15 shows the potential savings through the installation of a VSD for a 5.5 kW and a 18.5 kW motor operating for 8000 h/yr. In these cases, the payback can be from 18 months to 2 years. Table 4.15
Savings due to installation of variable speed drives Energy consumption 5.5 kW motor with no VSD
Energy consumption 5.5 kW motor with VSD
Energy consumption 18.5 kW motor with no VSD
Energy consumption 18.5 kW motor with VSD
Annual energy use (kW h)
44 000
35 200
148 000
118 400
Annual energy cost
$3520
$2816
$11 840
$9472
$704
$2368
Annual energy saving Cost of VSD Payback
$1295
$3460
1.8 years
1.5 years
Source: Teco Australia 2003 Assumptions: 8000 operating hours per year; 20% reduction in energy consumption due to VSD; electricity cost $0.08/kW h
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ECO-EFFICIENCY FOR THE DAIRY PROCESSING INDUSTRY
Variable speed drive on cooling tower fans: National Foods Ltd, Murray Bridge National Foods in Murray Bridge installed variable speed (frequency) drives on the fan motors of the refrigeration system water cooling towers. The fan motors were not required to be run at all times. Savings in energy consumption resulted (but were not quantified). The modification needed to be performed during low demand for refrigeration so that production requirements were not disrupted.
4.4.5
Lighting Around 4–6% of total electricity consumption is used for lighting in dairy processing plants (Kjaergaard-Jensen 1999). Different styles of lighting are available for different purposes, and they have varying efficiencies. Some types of lighting and their uses are listed below, from most to least energy-efficient (DSIR 2001b). Low-pressure sodium: This is the most efficient type of lamp at present. It is most suited to exterior lighting and emits yellow light. High-pressure sodium: These are not as energy-efficient as low-pressure sodium lights. They are suitable for internal and external use where colour rendition is not important. Metal halide and mercury vapour: These are commonly used for high-bay factory lighting, and emit a bluish-white light. Metal halide is 25% more efficient than mercury vapour lighting. Two types of metal halide lighting are available — standard and pulse start. Pulse start lights are more efficient and start more quickly. Fluorescent: These are the most efficient type for lighting small areas with low ceilings, or for task-level lighting. Fluorescent lights are available as a standard long lamp or in a compact style, which can be used as a direct replacement for incandescent lamps. The initial cost is higher, but the lamps use one-fifth the electricity and last up to 10 times as long. Standard 40 W fluorescent tubes can be replaced with 36 W high-density tri-phosphor tubes, which are 20% more efficient and produce 15% more light. Tungsten halogen lamps: These lamps are cheap to purchase but have high operating costs. They are useful for floodlighting. Miniature dichroic down lights: These are often used in reception areas and restaurants. Their energy efficiency is inferior to that of fluorescent lights and they should be avoided if energy consumption is a priority. Incandescent lamps: These are the least efficient, and although they have a low purchase cost they will end up costing more in the long run because of higher operating costs and lower product life.
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67
Table 4.16
Comparison of different types of lighting Incandescent
Tungsten
Halogen
240 V
6–12 V
Cheap
Low
Relative operating costs
High
Luminous efficacy
Capital cost
Wattage (lm/W)
Fluorescent
Metal halide
Sodium colourimproved
Low/ medium
Low/ medium
High
High
High
Medium
Low
Very low
Medium
10–20
22
30–50
Up to 70
60–115
40–44
15–1500
50–2000
10–75
8–36
35–3500
35–3500
1000
2000
2000– 45 000
8000– 10 000
6000-8000
12 000– 15 000
Very little
100 000–3 000 000
0.01–4.0
Solution clarification; removal of bacteria
Ultrafiltration
10 000–150 000
0.005–0.1
Protein, whey, milk concentration; clarification
Nanofiltration
150–20 000
0.0008–0.009
Lactose rejection, Protein, whey, milk concentration; recovery of caustic from CIP; standardisation of protein; desalinisation of salty whey
Reverse osmosis
